feat: implement tags filter in service layer

- Add TagsFilter string to SearchParams struct
- Update dbParams building to include tags_filter
- Add tags case to SearchFieldValues service for autocomplete
- Handle SearchTagsValues query results

Enables the backend service layer to process tag filtering requests
and provide autocomplete suggestions for tag values.

Relates to IMPLEMENTATION_TAGS_FILTER.md Phase 2

internal/services/search.go

@@ -25,6 +25,7 @@ type SearchParams struct {
 	AuthorFilter   string
 	SeriesFilter   string
 	GenreFilter    string
+	TagsFilter     string
 	LanguageFilter string
 	YearMin        int
 	YearMax        int
@@ -69,6 +70,7 @@ func (s *SearchService) SearchMediaItemsUnified(ctx context.Context, params Sear
 		AuthorFilter:   pgtype.Text{String: params.AuthorFilter, Valid: true},
 		SeriesFilter:   pgtype.Text{String: params.SeriesFilter, Valid: true},
 		GenreFilter:    pgtype.Text{String: params.GenreFilter, Valid: true},
+		TagsFilter:     pgtype.Text{String: params.TagsFilter, Valid: true},
 		LanguageFilter: pgtype.Text{String: params.LanguageFilter, Valid: true},
 		YearMin:        pgtype.Int4{Int32: int32(params.YearMin), Valid: true},
 		YearMax:        pgtype.Int4{Int32: int32(params.YearMax), Valid: true},
@@ -150,6 +152,23 @@ func (s *SearchService) SearchFieldValues(ctx context.Context, params FieldSearc
 		}
 		return fieldValues, nil
 
+	case "tags":
+		results, err := s.db.SearchTagsValues(ctx, database.SearchTagsValuesParams{
+			SearchQuery: pgtype.Text{String: params.SearchQuery, Valid: true},
+			UserID:      params.UserID,
+			LibraryID:   params.LibraryID,
+			Limit:       pgtype.Int4{Int32: int32(params.Limit), Valid: true},
+			Offset:      pgtype.Int4{Int32: int32(params.Offset), Valid: true},
+		})
+		if err != nil {
+			return nil, err
+		}
+		fieldValues := make([]FieldValue, len(results))
+		for i, r := range results {
+			fieldValues[i] = FieldValue{Value: r.Value, Count: r.Count, Score: r.Score}
+		}
+		return fieldValues, nil
+
 	case "series":
 		results, err := s.db.SearchSeriesValues(ctx, database.SearchSeriesValuesParams{
 			SearchQuery: pgtype.Text{String: params.SearchQuery, Valid: true},