Feature: Parallele Bild-Uploads, Heartbeat last_seen, Admin zuletzt aktiv, SW by-v1071

- Tagebuch: Bilder werden parallel hochgeladen (Promise.all), Button zeigt Fortschritt
- Auth: /heartbeat Route ergänzt — aktualisiert last_seen alle 5 Min
- Admin: last_seen + last_login in Nutzer-Liste angezeigt (🟢/🔵/⚪)
- Bump SW by-v1071

backend/routes/admin.py

@@ -359,7 +359,7 @@ async def list_users(
             SELECT u.id, u.name, {_email_col}, u.rolle, u.is_premium,
                    u.is_moderator, u.is_banned, u.ban_reason,
                    u.is_founder, u.is_partner, u.founder_number,
-                   u.created_at, u.last_login, u.subscription_tier,
+                   u.created_at, u.last_login, u.last_seen, u.subscription_tier,
                    (SELECT COUNT(*) FROM dogs d WHERE d.user_id=u.id) AS dog_count,
                    (SELECT COUNT(*) FROM forum_threads t WHERE t.user_id=u.id AND t.is_deleted=0) AS thread_count,
                    ROUND(COALESCE((SELECT SUM(r.distanz_km) FROM routes r WHERE r.user_id=u.id), 0), 1) AS total_km,