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/api/healthz/route.ts

@@ -0,0 +1,37 @@
+import { readFileSync } from "node:fs";
+import path from "node:path";
+
+export const runtime = "nodejs";
+export const dynamic = "force-dynamic";
+
+/**
+ * Deploy health check: reports which release is running. The deploy script
+ * writes `release.json` next to the server (in the standalone root) and polls
+ * this route after switching `current`; a mismatch or an unreachable server
+ * triggers the automatic rollback.
+ *
+ * In a dev checkout there is no release.json — the route answers with the
+ * commit baked into the environment, or "dev".
+ */
+export async function GET() {
+  let release: { commit?: string; short?: string; builtAt?: string; release?: string } | null = null;
+  try {
+    release = JSON.parse(readFileSync(path.join(process.cwd(), "release.json"), "utf8"));
+  } catch {
+    release = null;
+  }
+
+  const commit = release?.commit ?? process.env.FREEZMO_COMMIT ?? "dev";
+  return Response.json(
+    {
+      ok: true,
+      commit,
+      short: release?.short ?? commit.slice(0, 7),
+      builtAt: release?.builtAt ?? null,
+      release: release?.release ?? null,
+      dev: commit === "dev",
+      uptimeSeconds: Math.round(process.uptime()),
+    },
+    { headers: { "Cache-Control": "no-store" } },
+  );
+}

app/layout.tsx

@@ -5,6 +5,9 @@ import { InstallSheet } from "@/components/InstallSheet";
 import { OfflineBanner } from "@/components/OfflineBanner";
 import { ServiceWorkerRegistrar } from "@/components/ServiceWorkerRegistrar";
 import { Toaster } from "@/components/Toaster";
+import { IS_DEV_INSTANCE } from "@/lib/dev-mode";
+
+const devInstanceJs = IS_DEV_INSTANCE ? "true" : "false";
 import "./globals.css";
 
 export const metadata: Metadata = {
@@ -33,7 +36,12 @@ export const metadata: Metadata = {
       { url: "/icons/splash-1668x2388.png", media: "(device-width: 834px) and (device-height: 1194px) and (-webkit-device-pixel-ratio: 2)" },
     ],
   },
-  icons: {
+  icons: IS_DEV_INSTANCE
+    ? {
+        // Dev wears its own favicon so the two instances are never confused.
+        icon: [{ url: "/icons/dev-favicon.svg", type: "image/svg+xml" }],
+      }
+    : {
     icon: [
       // ?v=2 busts browser favicon caches after the icon redesign.
       { url: "/icons/favicon-32.png?v=2", sizes: "32x32", type: "image/png" },
@@ -62,10 +70,12 @@ export const viewport: Viewport = {
   // font-size rule in globals.css stops iOS Safari's focus auto-zoom, which
   // ignores the viewport meta anyway.
   viewportFit: "cover",
-  themeColor: [
-    { media: "(prefers-color-scheme: light)", color: "#f4f7fd" },
-    { media: "(prefers-color-scheme: dark)", color: "#0e1424" },
-  ],
+  themeColor: IS_DEV_INSTANCE
+    ? [{ media: "(prefers-color-scheme: light)", color: "#b45309" }, { media: "(prefers-color-scheme: dark)", color: "#b45309" }]
+    : [
+        { media: "(prefers-color-scheme: light)", color: "#f4f7fd" },
+        { media: "(prefers-color-scheme: dark)", color: "#0e1424" },
+      ],
 };
 
 /**
@@ -73,7 +83,7 @@ export const viewport: Viewport = {
  * `theme-color` meta in step with the *app* theme (the SSR metas follow the
  * OS preference, which is wrong once the user has picked a theme here).
  */
-const themeScript = `(function(){try{var s=localStorage.getItem('freezmo.theme');var d=s?s==='dark':window.matchMedia('(prefers-color-scheme: dark)').matches;if(d)document.documentElement.classList.add('dark');var l=localStorage.getItem('freezmo.locale.v1');if(l==='cs'||l==='en')document.documentElement.lang=l;var m=document.querySelector('meta[name="theme-color"][data-app]');if(!m){m=document.createElement('meta');m.setAttribute('name','theme-color');m.setAttribute('data-app','1');document.head.insertBefore(m,document.head.firstChild);}m.setAttribute('content',d?'#0e1424':'#f4f7fd');}catch(e){}})();`;
+const themeScript = `(function(){try{var DEV=${devInstanceJs};var s=localStorage.getItem('freezmo.theme');var d=s?s==='dark':window.matchMedia('(prefers-color-scheme: dark)').matches;if(d)document.documentElement.classList.add('dark');var l=localStorage.getItem('freezmo.locale.v1');if(l==='cs'||l==='en')document.documentElement.lang=l;var m=document.querySelector('meta[name="theme-color"][data-app]');if(!m){m=document.createElement('meta');m.setAttribute('name','theme-color');m.setAttribute('data-app','1');document.head.insertBefore(m,document.head.firstChild);}m.setAttribute('content',DEV?'#b45309':(d?'#0e1424':'#f4f7fd'));}catch(e){}})();`;
 
 /**
  * Captures Chrome's `beforeinstallprompt` (it can fire before React hydrates)

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",