feat: contact page improvements, Yandex map from addresses

- Instagram field: @username input with API validation (like team page)
- Phone validation: blocks auto-save when incomplete, shows warning
- SectionEditor: validate prop to conditionally block saves
- Yandex Map: auto-generated from addresses via Nominatim geocoding,
  dark theme, no API key needed
- Schedule: address hint linking to Contacts
- Renamed "Всплывающие окна" → "Формы записи", moved after Записи

src/app/admin/_components/SectionEditor.tsx

@@ -8,6 +8,8 @@ interface SectionEditorProps<T> {
   sectionKey: string;
   title: string;
   defaultData?: Partial<T>;
+  /** Return true if data is valid and can be saved. Blocks auto-save when false. */
+  validate?: (data: T) => boolean;
   children: (data: T, update: (data: T) => void) => React.ReactNode;
 }
 
@@ -17,6 +19,7 @@ export function SectionEditor<T>({
   sectionKey,
   title,
   defaultData,
+  validate,
   children,
 }: SectionEditorProps<T>) {
   const [data, setData] = useState<T | null>(null);
@@ -67,6 +70,7 @@ export function SectionEditor<T>({
 
     if (timerRef.current) clearTimeout(timerRef.current);
     timerRef.current = setTimeout(() => {
+      if (validate && !validate(data)) return;
       save(data);
     }, DEBOUNCE_MS);