fix: gocritic linter issues (appendAssign, ifElseChain, regexpMust)

backend/handlers/bookings/admin_reserve.go

@@ -88,7 +88,8 @@ func AdminReserveSlotHandler(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		var err error
-		allIDs := append(req.ServiceIDs, req.CustomServiceIDs...)
+		allIDs := append([]string{}, req.ServiceIDs...)
+		allIDs = append(allIDs, req.CustomServiceIDs...)
 		svcDuration, err = calculateServiceDurationWithOverrides(r.Context(), allIDs, req.ServiceOverrides)
 		if err != nil {
 			log.Printf("Failed to calculate duration: %v", err)

backend/handlers/bookings/manage.go

@@ -646,7 +646,8 @@ func AdminCreateBookingForUserHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Check for overlapping confirmed/in_progress/completed bookings
-	allIDs := append(req.ServiceIDs, req.CustomServiceIDs...)
+	allIDs := append([]string{}, req.ServiceIDs...)
+	allIDs = append(allIDs, req.CustomServiceIDs...)
 	var dur int
 	err := db.Conn.QueryRow(r.Context(), `
 		SELECT COALESCE(SUM(dur), 0) FROM (

backend/handlers/portfolio/images.go

@@ -30,6 +30,9 @@ import (
 
 const MaxInputLength = 256
 
+var filterRegexp = regexp.MustCompile(`^filter\[(.+)\]$`)
+var timestampRegexp = regexp.MustCompile(`^\d{15,20}$`)
+
 func mimeTypeForField(fieldName string) string {
 	switch fieldName {
 	case "file_full_avif", "file_thumb_avif":
@@ -173,11 +176,9 @@ func ListImages(w http.ResponseWriter, r *http.Request) {
 		if len(values) == 0 || values[0] == "" {
 			continue
 		}
-		match, _ := regexp.Compile(`^filter\[(.+)\]$`)
-		if match != nil {
-			matches := match.FindStringSubmatch(key)
-			if len(matches) == 2 {
-				category := matches[1]
+		match := filterRegexp.FindStringSubmatch(key)
+		if len(match) == 2 {
+			category := match[1]
 				value := values[0]
 
 				// Validate category exists
@@ -193,17 +194,17 @@ func ListImages(w http.ResponseWriter, r *http.Request) {
 				}
 
 				filterClauses.WriteString(fmt.Sprintf(" AND $%d::text = ANY(tag_names)", len(filterArgs)+1))
-				filterArgs = append(filterArgs, category+":"+value)
-			}
+			filterArgs = append(filterArgs, category+":"+value)
 		}
 	}
-
+	
 	var query string
 	var args []any
 
 	const formatCols = `, full_avif_url, full_webp_url, full_jpg_url, full_jxl_url, thumb_avif_url, thumb_webp_url, thumb_jpg_url`
 
-	if tagsFilter != "" {
+	switch {
+	case tagsFilter != "":
 		tagList := strings.Split(tagsFilter, ",")
 		cleanTags := make([]string, len(tagList))
 		for i, t := range tagList {
@@ -255,7 +256,7 @@ func ListImages(w http.ResponseWriter, r *http.Request) {
 		}
 		queryArgs[len(filterArgs)+len(cleanTags)+len(cursorArgs)] = limit
 		args = queryArgs
-	} else if tagFilter != "" {
+	case tagFilter != "":
 		argOffset := len(filterArgs)
 		searchPattern := "%" + tagFilter + "%"
 		searchIdx := argOffset + 1
@@ -289,7 +290,7 @@ func ListImages(w http.ResponseWriter, r *http.Request) {
 		}
 		queryArgs[searchIdx+len(cursorArgs)] = limit
 		args = queryArgs
-	} else {
+	default:
 		argOffset := len(filterArgs)
 		query = fmt.Sprintf(`
 			SELECT id, url, thumbnail_url, tag_names, created_at%s, 0 as match_count, 0.0 as relevance
@@ -1098,8 +1099,7 @@ func GetImage(w http.ResponseWriter, r *http.Request) {
 
 	// Lookup by timestamp (nanosecond Unix epoch from URL)
 	// Only allow numeric timestamps to prevent pattern enumeration
-	timestampMatch, _ := regexp.Compile(`^\d{15,20}$`)
-	if !timestampMatch.MatchString(imageID) {
+	if !timestampRegexp.MatchString(imageID) {
 		log.Printf("Invalid image ID format: %s", imageID)
 		http.Error(w, "Image not found", http.StatusNotFound)
 		return