feat: MVP-4 Sprint 1 - Query parser, real-time search, keyboard navigation

- Add query-parser.ts with AST for type:, tag:, is:favorite, is:pinned filters
- Integrate parser into search API
- Add real-time search with 300ms debounce in search-bar
- Add keyboard navigation (↑↓ Enter ESC) for Spotlight-like UX
- Add dropdown results display with loading state
- Add 22 tests for query parser

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/api/search/route.ts

@@ -1,15 +1,15 @@
 import { NextRequest } from 'next/server'
 import { searchNotes } from '@/lib/search'
+import { parseQuery } from '@/lib/query-parser'
 import { createErrorResponse, createSuccessResponse } from '@/lib/errors'
 
 export async function GET(req: NextRequest) {
   try {
     const { searchParams } = new URL(req.url)
     const q = searchParams.get('q') || ''
-    const type = searchParams.get('type') || undefined
-    const tag = searchParams.get('tag') || undefined
 
-    const notes = await searchNotes(q, { type, tag })
+    const queryAST = parseQuery(q)
+    const notes = await searchNotes(queryAST.text, queryAST.filters)
 
     return createSuccessResponse(notes)
   } catch (error) {