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/quick-add.tsx

@@ -0,0 +1,114 @@
+'use client'
+
+import { useState, useRef, useEffect } from 'react'
+import { useRouter } from 'next/navigation'
+import { toast } from 'sonner'
+import { Input } from '@/components/ui/input'
+import { cn } from '@/lib/utils'
+import { Plus, Loader2 } from 'lucide-react'
+
+export function QuickAdd() {
+  const [value, setValue] = useState('')
+  const [isLoading, setIsLoading] = useState(false)
+  const [isExpanded, setIsExpanded] = useState(false)
+  const inputRef = useRef<HTMLInputElement>(null)
+  const router = useRouter()
+
+  const handleSubmit = async (e?: React.FormEvent) => {
+    e?.preventDefault()
+    if (!value.trim() || isLoading) return
+
+    setIsLoading(true)
+    try {
+      const response = await fetch('/api/notes/quick', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ text: value }),
+      })
+
+      if (!response.ok) {
+        const error = await response.json()
+        throw new Error(error.error || 'Error creating note')
+      }
+
+      const note = await response.json()
+      toast.success('Nota creada', {
+        description: note.title,
+      })
+      setValue('')
+      setIsExpanded(false)
+      router.refresh()
+    } catch (error) {
+      toast.error('Error', {
+        description: error instanceof Error ? error.message : 'No se pudo crear la nota',
+      })
+    } finally {
+      setIsLoading(false)
+    }
+  }
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Enter' && !e.shiftKey) {
+      e.preventDefault()
+      handleSubmit()
+    }
+    if (e.key === 'Escape') {
+      setValue('')
+      setIsExpanded(false)
+      inputRef.current?.blur()
+    }
+  }
+
+  // Focus on keyboard shortcut
+  useEffect(() => {
+    const handleGlobalKeyDown = (e: KeyboardEvent) => {
+      if (e.key === 'n' && (e.metaKey || e.ctrlKey)) {
+        e.preventDefault()
+        inputRef.current?.focus()
+        setIsExpanded(true)
+      }
+    }
+    window.addEventListener('keydown', handleGlobalKeyDown)
+    return () => window.removeEventListener('keydown', handleGlobalKeyDown)
+  }, [])
+
+  return (
+    <form onSubmit={handleSubmit} className="flex items-center gap-2">
+      <div className="relative">
+        <Input
+          ref={inputRef}
+          type="text"
+          placeholder="cmd: título #tag..."
+          value={value}
+          onChange={(e) => setValue(e.target.value)}
+          onKeyDown={handleKeyDown}
+          onFocus={() => setIsExpanded(true)}
+          className={cn(
+            'w-48 transition-all duration-200',
+            isExpanded && 'w-72'
+          )}
+          disabled={isLoading}
+        />
+        {isLoading && (
+          <Loader2 className="absolute right-2 top-1/2 -translate-y-1/2 h-4 w-4 animate-spin text-muted-foreground" />
+        )}
+      </div>
+      <button
+        type="submit"
+        disabled={!value.trim() || isLoading}
+        className={cn(
+          'inline-flex items-center justify-center rounded-lg border bg-background p-2',
+          'hover:bg-accent hover:text-accent-foreground',
+          'disabled:pointer-events-none disabled:opacity-50',
+          'transition-colors'
+        )}
+      >
+        {isLoading ? (
+          <Loader2 className="h-4 w-4 animate-spin" />
+        ) : (
+          <Plus className="h-4 w-4" />
+        )}
+      </button>
+    </form>
+  )
+}