Media-Previews: _preview.jpg bei Upload, alle Listenansichten — SW by-v437, APP_VER 416

- media_utils: generate_preview() (Pillow, max 800px, JPEG q72) + preview_url_from()
- diary.py: Preview beim Bild-Upload, preview_url in media_items + cover_preview_url
  in Kalender-, Karten- und Listenabfragen
- forum.py: Preview in _save_upload(), foto_preview_url in Thread-Listen
- Frontend diary.js: cover_preview_url in Listenansicht, Mediengalerie, Kalender,
  Karten-Marker + Popup; onerror-Fallback auf Original
- Frontend forum.js: foto_preview_url in Thread-Karten-Thumbnails
- Admin: 'Previews generieren (Bestand)' Button → POST /admin/media/generate-previews

backend/routes/forum.py

@@ -8,7 +8,7 @@ from database import db
 from auth import get_current_user, get_current_user_optional
 from timeutils import safe_client_time
 from routes.push import send_push_to_user
-from media_utils import convert_media, extract_video_thumb
+from media_utils import convert_media, extract_video_thumb, generate_preview, preview_url_from
 
 logger = logging.getLogger(__name__)
 
@@ -87,6 +87,11 @@ def _save_upload(file: UploadFile, data: bytes) -> str:
         f.write(data)
     if ext in {".mp4", ".webm"}:
         extract_video_thumb(path)
+    else:
+        preview_bytes = generate_preview(data, ext)
+        if preview_bytes:
+            with open(os.path.splitext(path)[0] + "_preview.jpg", "wb") as f:
+                f.write(preview_bytes)
     return f"/media/forum/{filename}"
 
 def _parse_foto_urls(raw) -> list:
@@ -146,7 +151,9 @@ async def list_threads(
         for r in rows:
             t = dict(r)
             foto_list = _parse_foto_urls(t.get('foto_urls'))
-            t['foto_preview'] = foto_list[0] if foto_list else None
+            first = foto_list[0] if foto_list else None
+            t['foto_preview']         = first
+            t['foto_preview_url']     = preview_url_from(first)
             t['foto_urls'] = foto_list
             t['user_liked'] = _user_liked(conn, uid, 'thread', t['id']) if uid else False
             result.append(t)