Issue 17: StartOS 0.4.0 packaging

- Dockerfile: multi-stage build (Node frontend + Python backend)
- StartOS manifest, interfaces, backups, version graph
- start.sh: auto-generates session secret, creates first approver on boot
- Backend serves built frontend as SPA in production
- Single data volume for SQLite DB, platform backups cover it

deploy/startos/backups.ts

@@ -0,0 +1,5 @@
+import { sdk } from './sdk'
+
+export const { createBackup, restoreInit } = sdk.setupBackups(
+  async ({ effects }) => sdk.Backups.ofVolumes('main'),
+)