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/src/views/Register.vue

@@ -0,0 +1,37 @@
+<script setup>
+import { ref } from 'vue';
+import { useRouter } from 'vue-router';
+import { useAuthStore } from '../stores/auth';
+
+const email = ref('');
+const name = ref('');
+const password = ref('');
+const err = ref('');
+const router = useRouter();
+const auth = useAuthStore();
+
+async function submit() {
+  err.value = '';
+  try {
+    await auth.register(email.value, name.value, password.value);
+    router.push('/');
+  } catch (e) {
+    err.value = e.response?.data?.error || 'Registration failed';
+  }
+}
+</script>
+
+<template>
+  <div class="auth-wrap card">
+    <h1>Create account</h1>
+    <p class="muted">Start your collaborative workspace.</p>
+    <form @submit.prevent="submit" style="display: grid; gap: 10px">
+      <input v-model="name" placeholder="Display name" required />
+      <input v-model="email" type="email" placeholder="Email" required />
+      <input v-model="password" type="password" placeholder="Password (min 8 chars)" required minlength="8" />
+      <button type="submit">Register</button>
+    </form>
+    <p v-if="err" style="color: red">{{ err }}</p>
+    <p class="muted">Have an account? <router-link to="/login">Log in</router-link></p>
+  </div>
+</template>