Infra: split dev and production (releases, services, deploy script)

- Production now runs from ~/freezmo-prod/current (release symlink) as a
  standalone server on :3207; releases are exported by scripts/deploy.sh,
  built and e2e-verified on a temp port, switched atomically, health-
  checked via the new /api/healthz (commit + build time) and rolled back
  automatically on failure. Last 5 releases kept; scripts/rollback.sh for
  manual rollback. Shared env + data live in ~/freezmo-prod/shared/ and
  are symlinked into every release (existing sync/push data migrated and
  verified identical).
- Dev runs from ~/freezmo via freezmo-dev.service: next dev on :3217
  (LAN only), its own build folder (.next-dev via NEXT_DIST_DIR), its own
  data (~/freezmo/.freezmo-dev), DEV badge, dev favicon/theme colour,
  "Freezmo Dev" PWA identity and never the production service worker.
- /api/healthz + the Settings Details version row (short commit + build
  time). output: standalone in next.config (next start still works).
- AGENTS.md documents the workflow rules: only dev updates during a task,
  temporary dirs/ports for test builds, and deploy-at-the-end as the only
  production path. README gains an Environments and deploy section.
- Fix found by the rehearsal: lib/dev-mode.ts must not be a client module
  (a server component importing a constant from a "use client" module
  gets a truthy proxy, which baked dev metadata into production builds).
- SW -> freezmo-v34.

lib/dev-mode.ts

@@ -0,0 +1,7 @@
+/**
+ * True when this build is the development instance (`freezmo-dev.service`
+ * sets NEXT_PUBLIC_FREEZMO_DEV=1). Baked in at build/start time, so the dev
+ * server shows its badge, favicon, theme colour and PWA identity while a
+ * production build is completely unaffected.
+ */
+export const IS_DEV_INSTANCE = process.env.NEXT_PUBLIC_FREEZMO_DEV === "1";