feat: MVP-2 completion - search, quick add, backlinks, guided forms

## Search & Retrieval
- Improved search ranking with scoring (title match, favorites, recency)
- Highlight matches with excerpt extraction
- Fuzzy search with string-similarity
- Unified noteQuery function

## Quick Capture
- Quick Add API (POST /api/notes/quick) with type prefixes
- Quick add parser with tag extraction
- Global Quick Add UI (Ctrl+N shortcut)
- Tag autocomplete in forms

## Note Relations
- Automatic backlinks with sync on create/update/delete
- Backlinks API (GET /api/notes/[id]/backlinks)
- Related notes with scoring and reasons

## Guided Forms
- Type-specific form fields (command, snippet, decision, recipe, procedure, inventory)
- Serialization to/from markdown
- Tag suggestions based on content (GET /api/tags/suggest)

## UX by Type
- Command: Copy button for code blocks
- Snippet: Syntax highlighting with react-syntax-highlighter
- Procedure: Interactive checkboxes

## Quality
- Standardized error handling across all APIs
- Integration tests (28 tests passing)
- Unit tests for search, tags, quick-add

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

src/components/header.tsx

@@ -4,6 +4,7 @@ import Link from 'next/link'
 import { usePathname } from 'next/navigation'
 import { Button } from '@/components/ui/button'
 import { Plus, FileText, Settings } from 'lucide-react'
+import { QuickAdd } from '@/components/quick-add'
 
 export function Header() {
   const pathname = usePathname()
@@ -38,12 +39,15 @@ export function Header() {
             </Link>
           </nav>
         </div>
-        <Link href="/new">
-          <Button size="sm" className="gap-1.5">
-            <Plus className="h-4 w-4" />
-            Nueva nota
-          </Button>
-        </Link>
+        <div className="flex items-center gap-3">
+          <QuickAdd />
+          <Link href="/new">
+            <Button size="sm" className="gap-1.5">
+              <Plus className="h-4 w-4" />
+              Nueva nota
+            </Button>
+          </Link>
+        </div>
       </div>
     </header>
   )