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/db.py

@@ -2,21 +2,19 @@ from __future__ import annotations
 
 import pathlib
 import uuid
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 import aiosqlite
 
 from server.settings import settings
 
-SCHEMA_PATH = str(pathlib.Path(__file__).resolve().parents[1] / "tools" / "schema.sql")
-
 
 def new_id() -> str:
     return str(uuid.uuid4())
 
 
 def utc_now_iso() -> str:
-    return datetime.now(timezone.utc).replace(microsecond=0).isoformat()
+    return datetime.now(UTC).replace(microsecond=0).isoformat()
 
 
 async def get_db() -> aiosqlite.Connection:
@@ -27,6 +25,6 @@ async def get_db() -> aiosqlite.Connection:
 
 
 async def ensure_schema(db: aiosqlite.Connection) -> None:
-    schema = pathlib.Path(SCHEMA_PATH).read_text(encoding="utf-8")
-    await db.executescript(schema)
-    await db.commit()
+    from server.migrations import run_migrations
+
+    await run_migrations(db)