Perf: 9 Performance-Fixes — SW by-v1072

Backend:
- DB: 3 neue Indizes (forum_posts thread+user, routes user) — Forum/Routen-Queries
- Caching: cache.py (TTL-Cache ohne neue Dependency) für 5 statische Listen
  (training_exercises, pflege_tipps, wiki_stats, wiki_gruppen, help_articles)
- diary.py + breeder_photos.py: Bildverarbeitung (ffmpeg/PIL/EXIF) per
  run_in_executor → blockiert Event-Loop nicht mehr
- scheduler.py: 11 kollidierende Jobs auf 5-Min-Intervalle gestaggert, coalesce=True
- social.py: ORDER BY RANDOM() ohne LIMIT in 2 Stellen gefixt
- alerts.py: Haversine-Loop bekommt SQL-Bounding-Box-Vorfilter

Frontend:
- sw.js: Tile-Cache mit LRU-Eviction (max 500 Einträge)
- admin.js: Event-Listener-Leak — Tab-Klicks per Delegation statt N Listener
- api.js: compressImage() Helper — Client-seitiges Resize auf max 2000px
  (HEIC/Videos/<500KB unverändert), integriert in 8 Upload-Stellen
  (diary, dog-profile×2, walks, poison, lost, health×2)

Bump APP_VER 1071 → 1072 (sw.js, app.js, main.py, index.html)

backend/routes/breeder_photos.py

@@ -3,7 +3,7 @@ from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Form
 from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from typing import Optional
-import os, logging
+import os, logging, asyncio
 from database import db
 from auth import get_current_user, get_current_user_optional
 from media_utils import validate_upload, generate_preview
@@ -112,27 +112,37 @@ async def upload_photo(
         file_uuid = str(uuid.uuid4())
         file_path = os.path.join(save_dir, f"{file_uuid}.webp")
 
+        # Blockierende Bildverarbeitung in Threadpool auslagern,
+        # damit der Event-Loop für andere Requests frei bleibt.
+        loop = asyncio.get_event_loop()
+
+        def _write_bytes(p: str, data: bytes) -> None:
+            with open(p, "wb") as f:
+                f.write(data)
+
         # Thumbnail erzeugen
-        thumb_bytes = generate_preview(raw_data, ext)
+        thumb_bytes = await loop.run_in_executor(
+            None, lambda: generate_preview(raw_data, ext)
+        )
         thumb_path = None
         if thumb_bytes:
             thumb_path = os.path.join(save_dir, f"{file_uuid}_thumb.webp")
-            with open(thumb_path, "wb") as f:
-                f.write(thumb_bytes)
+            await loop.run_in_executor(None, lambda: _write_bytes(thumb_path, thumb_bytes))
 
-        # Originalbild konvertieren und speichern
-        # generate_preview liefert WebP, für das Original nehmen wir Pillow direkt
-        try:
-            import io
-            from PIL import Image, ImageOps
-            img = Image.open(io.BytesIO(raw_data))
-            img = ImageOps.exif_transpose(img)
-            img = img.convert("RGB")
-            img.save(file_path, format="WEBP", quality=85)
-        except Exception:
-            # Fallback: Rohdaten speichern
-            with open(file_path, "wb") as f:
-                f.write(raw_data)
+        # Originalbild konvertieren und speichern (Pillow direkt — WebP-Qualität 85)
+        def _save_original():
+            try:
+                import io
+                from PIL import Image, ImageOps
+                img = Image.open(io.BytesIO(raw_data))
+                img = ImageOps.exif_transpose(img)
+                img = img.convert("RGB")
+                img.save(file_path, format="WEBP", quality=85)
+            except Exception:
+                # Fallback: Rohdaten speichern
+                _write_bytes(file_path, raw_data)
+
+        await loop.run_in_executor(None, _save_original)
 
         # Relative Pfade für DB (relativ zu MEDIA_DIR)
         rel_file  = os.path.relpath(file_path,  MEDIA_DIR)