feat: overhaul with modular API, agent endpoints, migrations, backup and tests

- Split monolithic app.py into server/api/ routers
- Add Pydantic schemas for input validation
- Add /agent/* API with separate AGENT_TOKEN auth
- Replace static schema.sql with versioned migrations (datenerhaltend)
- Add tools/backup_db.py for SQLite backups
- Add Dockerfile HEALTHCHECK and compose.yml AGENT_TOKEN env
- Add pytest tests for user and agent API
- Update README with API docs and deployment safety notes
- Bump version to 1.2.0

server/ai.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import logging
-from datetime import datetime, timedelta
+from datetime import UTC, datetime, timedelta
 from typing import Any
 from zoneinfo import ZoneInfo
 
@@ -105,7 +105,7 @@ async def _recent_roasts(
     before_day: str,
     days: int = ROAST_HISTORY_DAYS,
 ) -> list[str]:
-    end = datetime.strptime(before_day, "%Y-%m-%d").date()
+    end = datetime.strptime(before_day, "%Y-%m-%d").replace(tzinfo=UTC).date()
     roasts: list[str] = []
     for offset in range(1, days + 1):
         day = (end - timedelta(days=offset)).isoformat()