feat(frontend): Vue 3 workspace UI with light/dark mode

- Vue 3 + Vite + Pinia + Vue Router, Axios client with JWT interceptor
- Auth views (login/register), dashboard with workspace switcher and search
- Nested PageTree sidebar, TipTap rich-text editor with debounced save
- Live collaboration via Socket.IO (remote updates, presence avatars, typing)
- Comments thread per page, invite-members card, member list
- Theme store (light/dark/system) persisted, CSS variables, ThemeToggle
- Multi-stage Dockerfile (build + nginx) for hosting

frontend/vite.config.js

@@ -0,0 +1,12 @@
+import { defineConfig } from 'vite';
+import vue from '@vitejs/plugin-vue';
+
+export default defineConfig({
+  plugins: [vue()],
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': { target: 'http://localhost:3000', changeOrigin: true },
+    },
+  },
+});