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/slots.py

@@ -6,7 +6,13 @@ from zoneinfo import ZoneInfo
 
 import aiosqlite
 
-from server.config_loader import MedsConfig, Slot, load_meds_config, slot_datetime, today_str
+from server.config_loader import (
+    MedsConfig,
+    Slot,
+    load_meds_config,
+    slot_datetime,
+    today_str,
+)
 from server.db import utc_now_iso