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>

package.json

@@ -15,6 +15,9 @@
     "dev:castle": "vite --host --config vite.castle.config.ts",
     "build:castle": "vue-tsc -b && vite build --config vite.castle.config.ts",
     "preview:castle": "vite preview --host --config vite.castle.config.ts",
+    "dev:chat": "vite --host --config vite.chat.config.ts",
+    "build:chat": "vue-tsc -b && vite build --config vite.chat.config.ts",
+    "preview:chat": "vite preview --host --config vite.chat.config.ts",
     "electron:dev": "concurrently \"vite --host\" \"electron-forge start\"",
     "electron:build": "vue-tsc -b && vite build && electron-builder",
     "electron:package": "electron-builder",