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.

components/AppHeader.tsx

@@ -6,6 +6,7 @@ import { useEffect, useState } from "react";
 import { SettingsDialog } from "@/components/SettingsDialog";
 import { TabBar } from "@/components/TabBar";
 import { ThemeToggle } from "@/components/ThemeToggle";
+import { IS_DEV_INSTANCE } from "@/lib/dev-mode";
 import { useI18n } from "@/lib/i18n";
 import { OPEN_SETTINGS_EVENT } from "@/lib/ui-events";
 import { cn } from "@/lib/utils";
@@ -61,6 +62,11 @@ export function AppHeader({ className, compact = false }: { className?: string;
             />
             <span className="flex min-w-0 items-baseline gap-2">
               <span className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">Freezmo</span>
+              {IS_DEV_INSTANCE ? (
+                <span className="rounded-md border border-amber-400/60 bg-amber-400/15 px-1.5 py-0.5 text-[10px] font-bold uppercase tracking-wide text-amber-700 dark:text-amber-300">
+                  DEV
+                </span>
+              ) : null}
               {!compact ? (
                 <span className="hidden truncate text-[13px] text-[var(--text-subtle)] sm:inline">
                   {t("header.tagline")}