feat(a11y): cross-platform hardening + modal focus-trap from impeccable audit

Responsive / viewport:
- add .min-h-viewport / .h-viewport utilities (100dvh + Telegram --tg-viewport-stable-height)
- migrate min-h-screen / h-screen / 100vh across 18 files
- reveal hover-only controls on focus-within + touch (desktop nav, admin settings)
- grid breakpoints (TopUpAmount, Contests), larger touch targets, nav aria-labels

Platform routing (Telegram WebView correctness):
- clipboard -> copyToClipboard util with execCommand fallback (10 files)
- window.open -> openTelegramLink / openLink (Profile, Referral, ChannelSubscriptionScreen)
- window.confirm -> useNativeDialog (admin pages); PromoOffersSection -> useDestructiveConfirm
- window.prompt -> usePrompt / PromptDialogHost (TipTap link editors)
- ESLint no-restricted-properties guard against regressions (adapters/clipboard util exempt)

Modal accessibility:
- new useFocusTrap hook (focus trap, Esc, scroll lock, focus restore)
- role=dialog / aria-modal / focus-trap: Polls, SuccessNotificationModal, AdminPolicies,
  AdminPromoGroups, AdminCampaigns, BroadcastPreview (Telegram + Email)
- new global usePrompt store + PromptDialogHost

src/store/promptDialog.ts

@@ -0,0 +1,60 @@
+import { create } from 'zustand';
+
+export interface PromptOptions {
+  /** Field label shown above the input. */
+  label: string;
+  /** Optional heading. */
+  title?: string;
+  initialValue?: string;
+  placeholder?: string;
+  submitLabel?: string;
+  cancelLabel?: string;
+  /** Input type, e.g. 'text' (default) or 'url'. */
+  inputType?: string;
+}
+
+interface PromptRequest extends PromptOptions {
+  resolve: (value: string | null) => void;
+}
+
+interface PromptState {
+  request: PromptRequest | null;
+  /**
+   * Open a prompt dialog and resolve with the entered value, or null if cancelled.
+   * Cross-platform replacement for window.prompt (which is unavailable in the Telegram WebView).
+   */
+  prompt: (options: PromptOptions) => Promise<string | null>;
+  submit: (value: string) => void;
+  cancel: () => void;
+}
+
+export const usePromptStore = create<PromptState>((set, get) => ({
+  request: null,
+
+  prompt: (options) =>
+    new Promise<string | null>((resolve) => {
+      // If a prompt is already open, cancel it before replacing.
+      const existing = get().request;
+      if (existing) existing.resolve(null);
+      set({ request: { ...options, resolve } });
+    }),
+
+  submit: (value) => {
+    const req = get().request;
+    if (!req) return;
+    req.resolve(value);
+    set({ request: null });
+  },
+
+  cancel: () => {
+    const req = get().request;
+    if (!req) return;
+    req.resolve(null);
+    set({ request: null });
+  },
+}));
+
+/** Returns a stable function that opens a prompt dialog and resolves with the value (or null). */
+export function usePrompt() {
+  return usePromptStore((s) => s.prompt);
+}