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

tools/migrations/001_initial.sql

@@ -0,0 +1,40 @@
+-- Migration 001: initial schema
+-- Idempotent via IF NOT EXISTS so it safely runs against existing databases.
+
+CREATE TABLE IF NOT EXISTS intake_log (
+  id TEXT PRIMARY KEY,
+  slot_id TEXT NOT NULL,
+  day TEXT NOT NULL,
+  status TEXT NOT NULL,
+  logged_at TEXT NOT NULL,
+  source TEXT DEFAULT 'app'
+);
+
+CREATE INDEX IF NOT EXISTS idx_intake_day ON intake_log(day);
+CREATE INDEX IF NOT EXISTS idx_intake_slot_day ON intake_log(slot_id, day);
+
+CREATE TABLE IF NOT EXISTS push_subscription (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  endpoint TEXT UNIQUE NOT NULL,
+  p256dh TEXT NOT NULL,
+  auth TEXT NOT NULL,
+  created_at TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS ai_cache (
+  key TEXT PRIMARY KEY,
+  content TEXT NOT NULL,
+  created_at TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS milestones (
+  id TEXT PRIMARY KEY,
+  unlocked_at TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS snooze (
+  slot_id TEXT NOT NULL,
+  day TEXT NOT NULL,
+  snooze_until TEXT NOT NULL,
+  PRIMARY KEY (slot_id, day)
+);