feat: add standalone chat PWA build

Adds a standalone encrypted chat PWA at chat.${domain}, built from
the existing src/modules/chat plugin. Same standalone pattern as
wallet/castle/activities:
- chat.html entry, vite.chat.config.ts (outDir: dist-chat,
  manifest id: chat-app, theme: green #16a34a — Anahata chakra)
- src/chat-app/{main.ts, app.ts, app.config.ts, App.vue} bootstraps
  base + chat only, with acceptTokenFromUrl for shared auth from hub
- npm run dev:chat / build:chat / preview:chat
- main app SW denylist extended with /chat/

Closes #20.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vite.config.ts

@@ -25,7 +25,7 @@ export default defineConfig(({ mode }) => ({
           '**/*.{js,css,html,ico,png,svg}'
         ],
         // Don't intercept standalone app paths — they have their own service workers
-        navigateFallbackDenylist: [/^\/sortir\//, /^\/castle\//],
+        navigateFallbackDenylist: [/^\/sortir\//, /^\/castle\//, /^\/chat\//],
       },
       includeAssets: [
         'favicon.ico',