feat: implement dynamic upload limits for exercise media

- Introduced role-based upload limits for exercise media, allowing users to upload up to 1 MB while admins and superadmins can upload up to 1024 MB.
- Updated the media upload logic to enforce these limits, enhancing the flexibility and control over media management in the application.

backend/routers/exercises.py

@@ -70,12 +70,23 @@ def normalize_exercise_skill_level(value) -> Optional[str]:
 
 MEDIA_ROOT = Path(os.getenv("MEDIA_ROOT", str(Path(__file__).resolve().parent.parent / "media")))
 MAX_EXERCISE_MEDIA = 10
-MAX_UPLOAD_BYTES = 50 * 1024 * 1024
+# Upload-Limits (Übungs-Medien): Trainer wie bisher kleiner; Admin/Superadmin höheres Limit für große Videos
+_MAX_UPLOAD_MB_USER = max(1, int(os.getenv("EXERCISE_MEDIA_MAX_UPLOAD_MB", "50")))
+_MAX_UPLOAD_MB_ADMIN = max(_MAX_UPLOAD_MB_USER, int(os.getenv("EXERCISE_MEDIA_ADMIN_MAX_UPLOAD_MB", "1024")))
+MAX_UPLOAD_BYTES_USER = _MAX_UPLOAD_MB_USER * 1024 * 1024
+MAX_UPLOAD_BYTES_ADMIN = _MAX_UPLOAD_MB_ADMIN * 1024 * 1024
 ALLOWED_UPLOAD_MIMES = frozenset(
     {"image/jpeg", "image/png", "image/gif", "video/mp4", "application/pdf"}
 )
 
 
+def _upload_limit_bytes(session: dict) -> int:
+    role = session.get("role") or ""
+    if role in ("admin", "superadmin"):
+        return MAX_UPLOAD_BYTES_ADMIN
+    return MAX_UPLOAD_BYTES_USER
+
+
 # ============================================================================
 # Pydantic Models
 # ============================================================================
@@ -1201,10 +1212,11 @@ async def upload_exercise_media(
             )
         else:
             raw = await file.read()
-            if len(raw) > MAX_UPLOAD_BYTES:
+            max_upload = _upload_limit_bytes(session)
+            if len(raw) > max_upload:
                 raise HTTPException(
                     status_code=413,
-                    detail=f"Datei zu groß (max. {MAX_UPLOAD_BYTES // (1024 * 1024)} MB)",
+                    detail=f"Datei zu groß (max. {max_upload // (1024 * 1024)} MB)",
                 )
             mime = file.content_type or ""
             if mime not in ALLOWED_UPLOAD_MIMES: