Stage 17: UI defect fixes (russian variant, Telegram theme/nav/banner, reconnect, hint zoom, plaque, history, transitions, per-game cache)

- #6 align the UI variant id to the backend canonical 'russian_scrabble' (type, variants, Lobby, mock, tests) — fixes the New->Russian 400
- #11/#12 inside Telegram force the colour scheme from WebApp.colorScheme (over OS prefers-color-scheme, fixing the Telegram Desktop breakage) and hide the theme switcher
- #14/#15 nav bar takes Telegram's bg; announcement banner gets a dedicated subtle --ad-bg accent token
- #16 suppress the reconnect banner while backgrounded and silently reconnect the live stream on return to the foreground
- #17 hint zoom scrolls to the placement's bounding box, not the top-left
- #19/#20 players plaque: active seat raised with side shadows, others sunk; tap toggles history
- #21/#23 history: scrollbar-gutter:stable (no word jitter); fixed-height drawer pins the bottom shadow to the board
- #3 (UI) disable nudge on the player's own turn
- #18a directional screen slide transitions (forward in from the right, back reveals the lobby)
- #13 per-game in-memory cache: instant render on re-entry + background refresh
- e2e: openGame waits for the slide transition to settle

ui/e2e/game.spec.ts

@@ -10,6 +10,10 @@ async function openGame(page: Page): Promise<void> {
   await page.getByRole('button', { name: /guest/i }).click();
   await page.getByRole('button', { name: /Ann/ }).click(); // the seeded active game vs Ann
   await expect(page.locator('[data-cell]').first()).toBeVisible();
+  // Wait for the screen-slide transition to settle so only the game pane remains;
+  // until it does, the leaving lobby pane's header (its menu button) is also in the
+  // DOM, which would make shared locators like .burger ambiguous.
+  await expect(page.locator('.pane')).toHaveCount(1);
 }
 
 test('placing a tile and confirming via 🏁 commits the move', async ({ page }) => {