multi-user: users, per-user profiles/filters/notifications, tab UI, apply forensics

* DB: users + user_profiles/filters/notifications/preferences; applications gets
  user_id + forensics_json + profile_snapshot_json; new errors table
  with 14d retention; schema versioning via MIGRATIONS list
* auth: password hashes in DB (argon2); env vars seed first admin; per-user
  sessions; CSRF bound to user id
* apply: personal info/WBS moved out of env into the request body; providers
  take an ApplyContext with Profile + submit_forms; full Playwright recorder
  (step log, console, page errors, network, screenshots, final HTML)
* web: five top-level tabs (Wohnungen/Bewerbungen/Logs/Fehler/Einstellungen);
  settings sub-tabs profil/filter/benachrichtigungen/account/benutzer;
  per-user matching, auto-apply and notifications (UI/Telegram/SMTP); red
  auto-apply switch on Wohnungen tab; forensics detail view for bewerbungen
  and fehler; retention background thread

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/retention.py

@@ -0,0 +1,24 @@
+"""Background thread that periodically prunes old logs / errors / forensics."""
+import logging
+import threading
+import time
+
+import db
+from settings import RETENTION_RUN_INTERVAL_SECONDS
+
+logger = logging.getLogger("web.retention")
+
+
+def _loop():
+    while True:
+        try:
+            db.cleanup_retention()
+        except Exception:
+            logger.exception("retention cleanup failed")
+        time.sleep(RETENTION_RUN_INTERVAL_SECONDS)
+
+
+def start() -> None:
+    t = threading.Thread(target=_loop, name="retention", daemon=True)
+    t.start()
+    logger.info("retention thread started (interval=%ss)", RETENTION_RUN_INTERVAL_SECONDS)