fix(ui+http): timezone validator + system-configs 404 noise

internal/http/system_configs.go

@@ -54,12 +54,14 @@ func (h *SystemConfigsHandler) handleList(w http.ResponseWriter, r *http.Request
 }
 
 func (h *SystemConfigsHandler) handleGet(w http.ResponseWriter, r *http.Request) {
-	locale := extractLocale(r)
 	key := r.PathValue("key")
 	val, err := h.store.Get(r.Context(), key)
 	if err != nil {
-		writeJSON(w, http.StatusNotFound, map[string]string{"error": i18n.T(locale, i18n.MsgNotFound, "config", key)})
-		return
+		// Fail-soft: settings-store "missing" = "empty". Returning 200 here
+		// stops Chrome from logging 404s for polled alert-state keys
+		// (e.g. alert.background.provider_error) that legitimately don't
+		// exist most of the time. Frontend treats empty as "no alert".
+		val = ""
 	}
 	writeJSON(w, http.StatusOK, map[string]string{"key": key, "value": val})
 }

ui/web/src/lib/timezone-utils.ts

@@ -78,12 +78,17 @@ export function getAllIanaTimezones(): TzOption[] {
   return _cachedTimezones;
 }
 
-let _cachedTzSet: Set<string> | undefined;
-
-/** Check if a value is a valid IANA timezone from the dynamic list. */
+/** Validate via Intl directly — accepts canonical + deprecated aliases that
+ * the browser's tz database knows (e.g. Asia/Saigon ↔ Asia/Ho_Chi_Minh).
+ * The earlier Set-based check rejected names whose canonical form differed
+ * from the user's stored value across browser/OS combos.
+ */
 export function isValidIanaTimezone(tz: string): boolean {
-  if (!_cachedTzSet) {
-    _cachedTzSet = new Set(getAllIanaTimezones().map((t) => t.value));
+  if (!tz) return false;
+  try {
+    new Intl.DateTimeFormat("en-US", { timeZone: tz });
+    return true;
+  } catch {
+    return false;
   }
-  return _cachedTzSet.has(tz);
 }