Add structured logging and better error handling

internal/server/settings_handlers.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"log/slog"
 	"net/http"
 
 	"ddc/internal/preferences"
@@ -18,14 +19,14 @@ func (server *Server) handleGetSettings(writer http.ResponseWriter, _ *http.Requ
 
 func (server *Server) handleUpdateSettings(writer http.ResponseWriter, request *http.Request) {
 	var body preferences.Preferences
-	if err := decodeJSON(request, &body); err != nil {
-		writeError(writer, http.StatusBadRequest, "invalid request body")
+	if !decodeBody(writer, request, &body) {
 		return
 	}
 	if err := server.manager.UpdatePreferences(body); err != nil {
-		writeFailure(writer, err)
+		writeFailure(writer, request, err)
 		return
 	}
+	slog.Info("settings updated", "request_id", requestIDFrom(request))
 	writeJSON(writer, http.StatusOK, server.settingsSnapshot())
 }