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.

app/manifest.ts

@@ -4,7 +4,35 @@ import type { MetadataRoute } from "next";
  * Web app manifest — what makes Freezmo installable on iOS/Android
  * (iOS reads the apple-* meta tags in app/layout.tsx as well).
  */
+const devInstance = process.env.NEXT_PUBLIC_FREEZMO_DEV === "1";
+
 export default function manifest(): MetadataRoute.Manifest {
+  if (devInstance) {
+    return {
+      // A distinct identity so the dev PWA installs next to the real one.
+      id: "/dev",
+      name: "Freezmo Dev — notes to study feed",
+      short_name: "Freezmo Dev",
+      description: "Development instance of Freezmo (hot reload). Not the production app.",
+      start_url: "/",
+      scope: "/",
+      display: "standalone",
+      display_override: ["standalone", "minimal-ui"],
+      orientation: "portrait",
+      background_color: "#1c1917",
+      theme_color: "#b45309",
+      categories: ["education", "productivity"],
+      icons: [
+        { src: "/icons/dev-icon.svg", sizes: "any", type: "image/svg+xml", purpose: "any" },
+        { src: "/icons/icon-512.png", sizes: "512x512", type: "image/png", purpose: "any" },
+      ],
+      shortcuts: [
+        { name: "New deck", short_name: "New", url: "/create" },
+        { name: "Library", short_name: "Library", url: "/" },
+      ],
+    };
+  }
+
   return {
     id: "/",
     name: "Freezmo — notes to study feed",