Correct daypart identity and display handling

internal/config/validate.go

@@ -5,6 +5,7 @@ import (
 	"net/url"
 	"strings"
 
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
 )
 
@@ -74,10 +75,16 @@ func Validate(cfg Config) error {
 	if len(cfg.Dayparts) == 0 {
 		return fmt.Errorf("dayparts must contain at least one entry")
 	}
+	daypartNames := make(map[string]int, len(cfg.Dayparts))
 	for i, daypart := range cfg.Dayparts {
 		if strings.TrimSpace(daypart.Name) == "" {
 			return fmt.Errorf("dayparts[%d].name is required", i)
 		}
+		key := forecast.CanonicalDaypartKey(daypart.Name)
+		if previous, exists := daypartNames[key]; exists {
+			return fmt.Errorf("dayparts[%d].name %q conflicts with dayparts[%d].name after canonicalization", i, daypart.Name, previous)
+		}
+		daypartNames[key] = i
 		if _, err := timeutil.ParseClock(daypart.Start); err != nil {
 			return fmt.Errorf("dayparts[%d].start is invalid: %w", i, err)
 		}