automatic DB maintenance: log rotation, orphan cleanup, VACUUM

The existing daily cleanup never effectively ran: it was an interval
job counted from container start (reset on every deploy), it called
asyncio.get_event_loop() from a worker thread, and even when deleting,
SQLite never returns freed pages to the filesystem. Live DB: 4.1 GB,
of which 2.6 GB log and 0.6 GB unused pages.

New maintenance service, scheduled daily at MAINTENANCE_HOUR_UTC:30
and once 5 minutes after every start:
- delete log entries older than LOG_RETENTION_DAYS (30) and keep at
  most LOG_MAX_ENTRIES (200k) newest ones
- delete processed_mails markers of deleted rules/accounts (FKs are
  not enforced by SQLite)
- VACUUM when >25% of the file is unused, only if free disk space
  covers the copy; never runs twice in parallel

GET/POST /api/logs/maintenance expose status and a manual run; the log
menu shows DB size, entry count and last run, with "Datenbank
aufräumen & verkleinern". Removed the dead cleanup_old_logs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/services/scheduler.py

@@ -1,6 +1,6 @@
 import asyncio
 import logging
-from datetime import datetime
+from datetime import datetime, timedelta
 
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from sqlalchemy.orm import Session
@@ -11,7 +11,8 @@ from app.models.db_models import Account, FilterRule, LogLevel, ProcessedMail
 from app.services.encryption import decrypt
 from app.services.filter_engine import evaluate_conditions, execute_action
 from app.services.imap_client import IMAPClient
-from app.services.log_service import cleanup_old_logs, write_log
+from app.services.log_service import write_log
+from app.services.maintenance import run_maintenance
 
 logger = logging.getLogger(__name__)
 
@@ -329,6 +330,13 @@ async def poll_account(account_id: int) -> None:
     await asyncio.to_thread(_poll_account_sync, account_id)
 
 
+async def maintenance_job() -> None:
+    try:
+        await asyncio.to_thread(run_maintenance)
+    except Exception:
+        pass  # bereits in run_maintenance geloggt
+
+
 def add_account_job(account: Account) -> None:
     job_id = f"poll_account_{account.id}"
     if scheduler.get_job(job_id):
@@ -364,12 +372,23 @@ def start_scheduler() -> None:
     finally:
         db.close()
 
-    # Täglicher Cleanup alter Logs
+    # DB-Wartung (Log-Rotation, VACUUM): täglich zu fester Uhrzeit — ein
+    # 24h-Intervall ab Start lief bei häufigen Deploys praktisch nie — und
+    # zusätzlich kurz nach jedem Start.
     scheduler.add_job(
-        lambda: asyncio.get_event_loop().run_in_executor(None, cleanup_old_logs, 30),
-        "interval",
-        hours=24,
-        id="cleanup_logs",
+        maintenance_job,
+        "cron",
+        hour=settings.maintenance_hour_utc,
+        minute=30,
+        timezone="UTC",
+        id="db_maintenance",
+        replace_existing=True,
+    )
+    scheduler.add_job(
+        maintenance_job,
+        "date",
+        run_date=datetime.now() + timedelta(minutes=5),
+        id="db_maintenance_startup",
         replace_existing=True,
     )