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/database.py

@@ -180,6 +180,8 @@ def init_db():
             anz_bewertungen INTEGER DEFAULT 0,
             created_at  TEXT    NOT NULL DEFAULT (datetime('now'))
         );
+        CREATE INDEX IF NOT EXISTS idx_routes_user ON routes(user_id, created_at DESC);
+
         CREATE TABLE IF NOT EXISTS route_walks (
             id         INTEGER PRIMARY KEY AUTOINCREMENT,
             user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
@@ -272,6 +274,8 @@ def init_db():
             created_at  TEXT    NOT NULL DEFAULT (datetime('now')),
             edited_at   TEXT
         );
+        CREATE INDEX IF NOT EXISTS idx_forum_posts_thread ON forum_posts(thread_id, created_at ASC);
+        CREATE INDEX IF NOT EXISTS idx_forum_posts_user   ON forum_posts(user_id, created_at DESC);
 
         -- PUSH SUBSCRIPTIONS (alternativ zu users.push_sub für mehrere Geräte)
         CREATE TABLE IF NOT EXISTS push_subscriptions (