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/admin.py

@@ -801,3 +801,47 @@ async def admin_delete_zuchter(zuchter_id: int, user=Depends(require_mod)):
             raise HTTPException(404, "Züchter nicht gefunden.")
         conn.execute("DELETE FROM wiki_zuchter WHERE id=?", (zuchter_id,))
         _audit(conn, user, "wiki_zuchter_delete", f"zuchter:{zuchter_id}")
+
+
+# ------------------------------------------------------------------
+# POST /api/admin/media/generate-previews — Previews für Bestandsmedien
+# ------------------------------------------------------------------
+@router.post("/media/generate-previews")
+async def generate_media_previews(user=Depends(require_admin)):
+    """Generiert fehlende _preview.jpg für alle Bilder in /data/media."""
+    import io as _io
+    from media_utils import generate_preview, _PREVIEW_EXTS
+    MEDIA_DIR = os.getenv("MEDIA_DIR", "/data/media")
+
+    generated = 0
+    skipped   = 0
+    errors    = 0
+
+    for subdir in ("diary", "forum"):
+        folder = os.path.join(MEDIA_DIR, subdir)
+        if not os.path.isdir(folder):
+            continue
+        for fname in os.listdir(folder):
+            # Nur Original-Bilder (keine _preview, _thumb, Videos, PDFs)
+            low = fname.lower()
+            if "_preview" in low or "_thumb" in low:
+                continue
+            base, ext = os.path.splitext(fname)
+            if ext.lower() not in _PREVIEW_EXTS:
+                continue
+            preview_path = os.path.join(folder, base + "_preview.jpg")
+            if os.path.exists(preview_path):
+                skipped += 1
+                continue
+            try:
+                data = open(os.path.join(folder, fname), "rb").read()
+                preview = generate_preview(data, ext)
+                if preview:
+                    open(preview_path, "wb").write(preview)
+                    generated += 1
+                else:
+                    skipped += 1
+            except Exception as exc:
+                errors += 1
+
+    return {"generated": generated, "skipped": skipped, "errors": errors}