feat: initial brainstorming app — Nuxt 3 + SQLite + admin auth

Nuxt 3 app with:
- SQLite (better-sqlite3) for persistence
- Anonymous idea submission and voting
- Admin auth with session cookies
- AI analysis via Gemini API
- Nuxt UI components + Tailwind

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/pages/login.vue

@@ -0,0 +1,37 @@
+<script setup lang="ts">
+const { login } = useAuth()
+const password = ref('')
+const error = ref('')
+
+async function submit() {
+  try {
+    error.value = ''
+    await login(password.value)
+    navigateTo('/admin')
+  } catch {
+    error.value = 'Contraseña incorrecta'
+  }
+}
+</script>
+
+<template>
+  <div class="min-h-screen flex items-center justify-center bg-neutral-50 p-4">
+    <UCard class="w-full max-w-sm">
+      <template #header>
+        <h1 class="text-xl font-bold text-center">Admin Login</h1>
+      </template>
+      <form class="space-y-4" @submit.prevent="submit">
+        <UFormField label="Contraseña">
+          <UInput v-model="password" type="password" placeholder="Contraseña de admin" />
+        </UFormField>
+        <p v-if="error" class="text-sm text-red-500">{{ error }}</p>
+        <UButton type="submit" block :disabled="!password">
+          Entrar
+        </UButton>
+      </form>
+      <template #footer>
+        <NuxtLink to="/" class="text-sm text-neutral-500 hover:underline">Volver al tablón</NuxtLink>
+      </template>
+    </UCard>
+  </div>
+</template>