feat: add standalone forum PWA build

Adds a standalone forum PWA at forum.${domain}, built from the
existing src/modules/forum plugin (NIP-72 communities + kind 1111
posts + voting). Same standalone pattern as the other modules:
- forum.html entry, vite.forum.config.ts (outDir: dist-forum,
  manifest id: forum-app, theme: blue #2563eb — Vishuddha chakra)
- src/forum-app/{main.ts, app.ts, app.config.ts, App.vue} bootstraps
  base + forum only, with acceptTokenFromUrl for shared auth from hub
- new ForumListPage view + /forum route added to the forum module
  (previously the list was only embedded in Home.vue)
- npm run dev:forum / build:forum / preview:forum
- main app SW denylist extended with /forum/, /submit/, /submission/

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:forum": "vite --host --config vite.forum.config.ts",
+    "build:forum": "vue-tsc -b && vite build --config vite.forum.config.ts",
+    "preview:forum": "vite preview --host --config vite.forum.config.ts",
     "electron:dev": "concurrently \"vite --host\" \"electron-forge start\"",
     "electron:build": "vue-tsc -b && vite build && electron-builder",
     "electron:package": "electron-builder",