feat: add media preview functionality to media library

- Introduced a preview feature for media assets, allowing users to view images and videos in a modal overlay.
- Updated the MediaLibraryPage component to handle media selection and display previews based on the media type.
- Enhanced CSS styles for media cards and preview modals to improve user experience and accessibility.
- Updated instructional text to guide users on how to access media previews.

frontend/src/app.css

@@ -5628,6 +5628,22 @@ a.analysis-split__nav-item {
   cursor: pointer;
   color: var(--text1);
 }
+.media-library__card-thumb-hit {
+  display: block;
+  width: 100%;
+  margin: 0;
+  padding: 0;
+  border: none;
+  background: transparent;
+  cursor: zoom-in;
+  text-align: left;
+  font: inherit;
+  color: inherit;
+  -webkit-tap-highlight-color: transparent;
+}
+.media-library__card-thumb-hit:active {
+  opacity: 0.96;
+}
 .media-library__card-thumb-wrap {
   aspect-ratio: 1;
   background: var(--surface2);
@@ -5717,6 +5733,21 @@ a.analysis-split__nav-item {
   overflow: hidden;
   background: var(--surface2);
 }
+.media-library__table-thumb-hit {
+  display: block;
+  margin: 0;
+  padding: 0;
+  border: none;
+  background: transparent;
+  cursor: zoom-in;
+  font: inherit;
+  border-radius: 8px;
+  -webkit-tap-highlight-color: transparent;
+}
+.media-library__table-thumb-hit:focus-visible {
+  outline: 2px solid var(--accent, #3b82f6);
+  outline-offset: 2px;
+}
 .media-library__table-thumb .media-library__thumb-img,
 .media-library__table-thumb .media-library__thumb-video {
   width: 56px;
@@ -5865,3 +5896,74 @@ a.analysis-split__nav-item {
   flex: 1 1 160px;
   min-width: 0;
 }
+
+/* Vorschau-Modal (Vollbild nah) */
+.media-library__overlay--preview {
+  background: rgba(0, 0, 0, 0.72);
+  z-index: 210;
+}
+.media-library__modal--preview {
+  max-width: min(92vw, 960px);
+  width: 100%;
+  max-height: min(94vh, 900px);
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+.media-library__modal--preview .media-library__modal-head {
+  flex-shrink: 0;
+}
+.media-library__preview-title {
+  flex: 1;
+  min-width: 0;
+  font-size: 1rem;
+  font-weight: 600;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  margin-right: 8px;
+}
+.media-library__modal--preview .media-library__modal-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+}
+.media-library__preview-head-actions {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  flex-shrink: 0;
+}
+.media-library__preview-body {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 12px 16px 20px;
+  background: var(--surface2);
+}
+.media-library__preview-img {
+  max-width: 100%;
+  max-height: min(78vh, 720px);
+  width: auto;
+  height: auto;
+  object-fit: contain;
+  border-radius: 8px;
+  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.12);
+}
+.media-library__preview-video {
+  width: 100%;
+  max-height: min(78vh, 720px);
+  border-radius: 8px;
+  background: #000;
+}
+.media-library__preview-fallback {
+  text-align: center;
+  padding: 24px 16px;
+  max-width: 360px;
+}
+.media-library__preview-fallback .btn {
+  margin-top: 12px;
+}

frontend/src/pages/MediaLibraryPage.jsx

@@ -80,6 +80,14 @@ function MediaThumb({ mediaId, mimeType }) {
   return <div className="media-library__thumb-ph">◆</div>
 }
 
+function previewDisplayKind(mimeType) {
+  const m = (mimeType || '').toLowerCase()
+  if (m.startsWith('image/')) return 'image'
+  if (m.startsWith('video/')) return 'video'
+  if (m.includes('pdf')) return 'pdf'
+  return 'other'
+}
+
 export default function MediaLibraryPage() {
   const { user } = useAuth()
   const isPlatformAdmin = user?.role === 'admin' || user?.role === 'superadmin'
@@ -102,6 +110,7 @@ export default function MediaLibraryPage() {
   const [bulkClubId, setBulkClubId] = useState('')
   const [bulkApplyVis, setBulkApplyVis] = useState(false)
   const [busy, setBusy] = useState(false)
+  const [preview, setPreview] = useState(null)
 
   const loadClubs = useCallback(async () => {
     try {
@@ -143,6 +152,15 @@ export default function MediaLibraryPage() {
     return () => clearTimeout(t)
   }, [lifecycle, q, loadItems])
 
+  useEffect(() => {
+    if (!preview) return
+    const onKey = (e) => {
+      if (e.key === 'Escape') setPreview(null)
+    }
+    window.addEventListener('keydown', onKey)
+    return () => window.removeEventListener('keydown', onKey)
+  }, [preview])
+
   const toggleSel = (id) => {
     setSelected((prev) => {
       const n = new Set(prev)
@@ -158,6 +176,7 @@ export default function MediaLibraryPage() {
   }
 
   const openEdit = (it) => {
+    setPreview(null)
     const p = it.permissions || {}
     setModal(it)
     setModalDraft({
@@ -299,8 +318,8 @@ export default function MediaLibraryPage() {
             </div>
           </div>
           <p className="media-library__intro">
-            Veröffentlichte Medien (Verein/Plattform) und eigene Uploads. Bearbeiten und Papierkorb über das
+            Veröffentlichte Medien (Verein/Plattform) und eigene Uploads. Vorschau: Bild oder Video groß
-            Menü pro Medium — Bulk unten in der Leiste.
+            anklicken. Bearbeiten und Papierkorb über das Menü pro Medium — Bulk unten in der Leiste.
           </p>
         </header>
 
@@ -397,9 +416,16 @@ export default function MediaLibraryPage() {
                   >
                     <MoreVertical size={20} />
                   </button>
-                  <div className="media-library__card-thumb-wrap">
+                  <button
-                    <MediaThumb mediaId={it.id} mimeType={it.mime_type} />
+                    type="button"
-                  </div>
+                    className="media-library__card-thumb-hit"
+                    onClick={() => setPreview(it)}
+                    title="Vorschau"
+                  >
+                    <div className="media-library__card-thumb-wrap">
+                      <MediaThumb mediaId={it.id} mimeType={it.mime_type} />
+                    </div>
+                  </button>
                   <div className="media-library__card-footer">
                     <div className="media-library__card-name" title={it.original_filename || `#${it.id}`}>
                       {it.original_filename || `Medium #${it.id}`}
@@ -439,9 +465,16 @@ export default function MediaLibraryPage() {
                         <input type="checkbox" checked={selected.has(it.id)} onChange={() => toggleSel(it.id)} />
                       </td>
                       <td className="media-library__td-thumb">
-                        <div className="media-library__table-thumb">
+                        <button
-                          <MediaThumb mediaId={it.id} mimeType={it.mime_type} />
+                          type="button"
-                        </div>
+                          className="media-library__table-thumb-hit"
+                          onClick={() => setPreview(it)}
+                          title="Vorschau"
+                        >
+                          <div className="media-library__table-thumb">
+                            <MediaThumb mediaId={it.id} mimeType={it.mime_type} />
+                          </div>
+                        </button>
                       </td>
                       <td className="media-library__td-name">{it.original_filename || `#${it.id}`}</td>
                       <td>{it.visibility}</td>
@@ -471,6 +504,99 @@ export default function MediaLibraryPage() {
         ) : null}
       </div>
 
+      {preview ? (
+        <div
+          className="media-library__overlay media-library__overlay--preview"
+          role="dialog"
+          aria-modal="true"
+          aria-labelledby="preview-media-title"
+          onClick={() => setPreview(null)}
+        >
+          <div
+            className="media-library__modal media-library__modal--preview"
+            onClick={(e) => e.stopPropagation()}
+          >
+            <div className="media-library__modal-head">
+              <h2 id="preview-media-title" className="media-library__preview-title">
+                {preview.original_filename || `Medium #${preview.id}`}
+              </h2>
+              <div className="media-library__preview-head-actions">
+                <button
+                  type="button"
+                  className="btn btn-secondary btn-small"
+                  onClick={() => {
+                    openEdit(preview)
+                  }}
+                >
+                  Bearbeiten
+                </button>
+                <button
+                  type="button"
+                  className="media-library__icon-btn"
+                  onClick={() => setPreview(null)}
+                  aria-label="Vorschau schließen"
+                >
+                  <X size={22} />
+                </button>
+              </div>
+            </div>
+            <div className="media-library__preview-body">
+              {(() => {
+                const url = resolveMediaAssetFileUrl(preview.id)
+                const kind = previewDisplayKind(preview.mime_type)
+                if (!url) {
+                  return <p className="media-library__hint">Keine Datei-URL.</p>
+                }
+                if (kind === 'image') {
+                  return (
+                    <img
+                      key={preview.id}
+                      className="media-library__preview-img"
+                      src={url}
+                      alt=""
+                    />
+                  )
+                }
+                if (kind === 'video') {
+                  return (
+                    <video
+                      key={preview.id}
+                      className="media-library__preview-video"
+                      src={url}
+                      controls
+                      playsInline
+                      preload="metadata"
+                    >
+                      Wiedergabe nicht unterstützt.
+                    </video>
+                  )
+                }
+                if (kind === 'pdf') {
+                  return (
+                    <div className="media-library__preview-fallback">
+                      <p className="media-library__hint">PDF — zur Ansicht im neuen Tab öffnen.</p>
+                      <a className="btn btn-secondary" href={url} target="_blank" rel="noopener noreferrer">
+                        PDF öffnen
+                      </a>
+                    </div>
+                  )
+                }
+                return (
+                  <div className="media-library__preview-fallback">
+                    <p className="media-library__hint">
+                      Vorschau für diesen Typ nicht verfügbar ({preview.mime_type || 'unbekannt'}).
+                    </p>
+                    <a className="btn btn-secondary" href={url} target="_blank" rel="noopener noreferrer">
+                      Datei öffnen
+                    </a>
+                  </div>
+                )
+              })()}
+            </div>
+          </div>
+        </div>
+      ) : null}
+
       {bulkOpen ? (
         <div className="media-library__overlay" role="dialog" aria-modal="true" aria-labelledby="bulk-title">
           <div className="media-library__modal media-library__modal--wide">