feat(07-01): add QuickAddItem migration, model, and query functions

- Create 003_quick_add_library.sql with quick_add_items table and user index
- Add QuickAddItem struct to models.go following Category pattern
- Add ListQuickAddItems, CreateQuickAddItem, UpdateQuickAddItem, DeleteQuickAddItem to queries.go

backend/internal/models/models.go

@@ -122,3 +122,13 @@ type TemplateDetail struct {
 	Template
 	Items []TemplateItem `json:"items"`
 }
+
+type QuickAddItem struct {
+	ID        uuid.UUID `json:"id"`
+	UserID    uuid.UUID `json:"user_id"`
+	Name      string    `json:"name"`
+	Icon      string    `json:"icon"`
+	SortOrder int       `json:"sort_order"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+}