feat(ui): paint VK status bar to the app theme (VKWebAppSetViewSettings)

Parity with the Telegram chrome painting: on a VK Mini App launch and on
every theme change, set VK's status-bar appearance (and, on Android, the
action/navigation bar colours) from the app's live theme tokens, so the VK
chrome matches the UI instead of clashing.

syncVKChrome mirrors syncTelegramChrome; the status-bar appearance is
derived from the --bg token's luminance (appearanceForBg, unit-tested).
Wired into the VK onScheme handler (fires on launch + on theme change) and
setTheme. Docs: UI_DESIGN VK integration.

ui/src/lib/vk.ts

@@ -198,3 +198,42 @@ export async function vkDisableSwipeBack(): Promise<void> {
     // Outside VK / unsupported: VK's default gesture handling stays as-is.
   }
 }
+
+/**
+ * appearanceForBg maps a background colour to the VK view appearance: a dark background wants the
+ * 'dark' appearance (light status-bar icons), a light one 'light'. It accepts a `#rgb` / `#rrggbb`
+ * string (the app's `--bg` token); anything unparseable defaults to 'light'. Pure, so it is
+ * unit-tested.
+ */
+export function appearanceForBg(bg: string): 'light' | 'dark' {
+  const hex = bg.trim().replace(/^#/, '');
+  const full = hex.length === 3 ? [...hex].map((c) => c + c).join('') : hex;
+  if (full.length !== 6 || /[^0-9a-fA-F]/.test(full)) return 'light';
+  const r = parseInt(full.slice(0, 2), 16);
+  const g = parseInt(full.slice(2, 4), 16);
+  const b = parseInt(full.slice(4, 6), 16);
+  // Rec. 601 luma; below the midpoint is a dark background.
+  return 0.299 * r + 0.587 * g + 0.114 * b < 128 ? 'dark' : 'light';
+}
+
+/**
+ * vkSetViewSettings paints VK's status bar — and, on Android, the action and navigation bars — to
+ * match the app. appearance is the VK status-bar appearance ('light' | 'dark'); actionBarColor and
+ * navigationBarColor are Android-only hex colours (ignored elsewhere). Best-effort; a no-op outside
+ * VK or on a client without the method.
+ */
+export async function vkSetViewSettings(
+  appearance: 'light' | 'dark',
+  actionBarColor: string,
+  navigationBarColor: string,
+): Promise<void> {
+  try {
+    await (await bridge()).send('VKWebAppSetViewSettings', {
+      status_bar_style: appearance,
+      action_bar_color: actionBarColor,
+      navigation_bar_color: navigationBarColor,
+    });
+  } catch {
+    // Outside VK / unsupported: the client keeps its default bars.
+  }
+}