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

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE = "tym-v1.1.0-914619f3";
+const CACHE = "tym-v1.2.0-914619f3";
 const ASSETS = [
   "/",
   "/index.html",

public/version.json

@@ -1,5 +1,5 @@
 {
-  "version": "1.1.0",
-  "buildTime": "2026-07-08T06:50:31.880953Z",
+  "version": "1.2.0",
+  "buildTime": "2026-09-21T10:33:11.129661Z",
   "buildHash": "914619f3"
 }