feat: add Search Dialog component

[amondnet]

Description

Implement a search dialog/modal for full-text search of Notion pages.

Reference

• ref/react-notion-x/packages/react-notion-x/src/components/search-dialog.tsx

Tasks

• Create SearchDialog.vue in packages/notion-nuxt-layer/app/components/
• Add search input with debounced queries
• Display search results with page titles
• Handle loading and error states
• Add keyboard navigation (Cmd+K to open)
• Integrate with existing /api/search-notion endpoint

Dependencies

• Existing search API endpoint
• @iconify/vue for icons