feat: add SearchService for unified search functionality

- Create SearchService with SearchMediaItemsUnified method
- Add SearchFieldValues method for autocomplete dropdown population
- Add parseSearchQuery helper for quote detection (exact vs fuzzy search)
- Move all business logic from handler to service layer
- Follow established service pattern (FiltersService, CollectionService)
- Service created inside handler constructor, not in main.go
- SearchParams struct supports all filter types + sort parameter
- FieldSearchParams struct for field-specific autocomplete queries
- Returns FieldValue results with count and similarity scores

This provides a clean service layer abstraction for search operations.

internal/services/search.go

@@ -30,6 +30,7 @@ type SearchParams struct {
 	YearMax        int
 	HasCover       bool
 	SearchQuery    string
+	Sort           string
 	Limit          int
 	Offset         int
 }
@@ -76,6 +77,7 @@ func (s *SearchService) SearchMediaItemsUnified(ctx context.Context, params Sear
 		SearchQuery:    pgtype.Text{String: searchQuery, Valid: true},
 		IsExactSearch:  pgtype.Bool{Bool: isExact, Valid: true},
 		SearchPattern:  pgtype.Text{String: searchPattern, Valid: isExact},
+		Sort:           pgtype.Text{String: params.Sort, Valid: true},
 		Limit:          pgtype.Int4{Int32: int32(params.Limit), Valid: true},
 		Offset:         pgtype.Int4{Int32: int32(params.Offset), Valid: true},
 	}