Dev workflow: network-bound vite dev + documented hot-reload loop

- 'npm run dev' now binds the network (vite dev --host) so the HMR dev server is
  reachable from another machine.
- README documents the two-terminal loop (serve --reload + npm run dev via the
  /api proxy), so iterating no longer needs build + restart + hard-refresh.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -4,7 +4,7 @@
   "version": "0.1.0",
   "type": "module",
   "scripts": {
-    "dev": "vite dev",
+    "dev": "vite dev --host",
     "build": "vite build",
     "preview": "vite preview"
   },