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>

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\//, /^\/forum\//, /^\/submit\//, /^\/submission\//],
       },
       includeAssets: [
         'favicon.ico',