feat: accept multiple formats for unlimited in user overrides

User can now input unlimited with:
- "unbegrenzt" (German)
- "unlimited" (English)
- "inf"
- "999999"
- "∞" (infinity symbol)

All map to NULL (unlimited) in database.

Updated legend to show:
- "unbegrenzt, inf, 999999" = Unbegrenzt
- Clear documentation for users

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/AdminUserRestrictionsPage.jsx

@@ -83,7 +83,11 @@ export default function AdminUserRestrictionsPage() {
     } else {
       // Parse value
       let parsedValue = null
-      if (value === 'unlimited' || value === '∞') {
+      const lowerValue = value.toLowerCase().trim()
+
+      // Accept multiple formats for unlimited
+      if (lowerValue === 'unlimited' || lowerValue === 'unbegrenzt' ||
+          value === '∞' || lowerValue === 'inf' || lowerValue === '999999') {
         parsedValue = null
       } else if (value === '0') {
         parsedValue = 0
@@ -495,8 +499,8 @@ export default function AdminUserRestrictionsPage() {
             <div style={{ marginTop: 8, display: 'flex', gap: 24, flexWrap: 'wrap' }}>
               <span><strong>Leer</strong> = Tier-Standard nutzen (kein Override)</span>
               <span><strong style={{ color: 'var(--danger)' }}>0</strong> = Feature deaktiviert</span>
-              <span><strong>∞ oder leer</strong> = Unbegrenzt (bei Count-Features)</span>
-              <span><strong>1-999999</strong> = Limit-Wert</span>
+              <span><strong>unbegrenzt, inf, 999999</strong> = Unbegrenzt</span>
+              <span><strong>1-999998</strong> = Limit-Wert</span>
             </div>
           </div>
         </>