feat(stats): per-game hints used + lifetime moves and hint share

Store the hints a player used in each game, and add two lifetime tiles —
Moves and Hint share — to the statistics screen.

- per-game: game_players.hints_used now counts EVERY hint (allowance + wallet),
  not just the free allowance, so it is the seat's true total hints used this
  game. The allowance decision (used < HintsPerPlayer) and the hint badge values
  (hints_remaining / wallet_balance) are unchanged — the lobby hint-count fix does
  NOT regress; only the admin "hints used" column, which silently under-counted
  wallet hints, becomes accurate.
- account_stats gains two summed counters: moves (the player's plays — passes and
  exchanges excluded) and hints_used (every hint). Computed at game finish in
  buildStats over the same non-guest, non-honest-AI games as the rest of the stats.
- wire: StatsView gains moves + hints_used (trailing); gateway + UI codec + model;
  regen.
- ui: two tiles (Moves, Hint share = hints_used/moves, one-decimal % in the active
  locale); card order games·wins·draws·losses·moves·hint-share·best game·win-rate.
- docs: ARCHITECTURE §9 + baseline comment, FUNCTIONAL (+ru), UI_DESIGN.

Tests: TestHintPolicy (hints_used counts the wallet hint), TestGameLifecycleAndStats
(moves>0, hints=0), gateway stats round-trip, UI hintShare unit + codec + e2e.

ui/e2e/social.spec.ts

@@ -58,6 +58,10 @@ test('stats screen shows the metrics and the per-variant best move', async ({ pa
   await page.getByRole('button', { name: /Stats/ }).click();
   await expect(page.getByText('Win rate')).toBeVisible();
   await expect(page.getByText('Best move')).toBeVisible();
+  // The Moves count and the derived Hint share (12 hints / 248 plays = 4.8%, one decimal).
+  await expect(page.getByText('Moves', { exact: true })).toBeVisible();
+  await expect(page.getByText('Hint share')).toBeVisible();
+  await expect(page.getByText('4.8%')).toBeVisible();
   // The best move breaks down per played variant, each row labelled by the variant and
   // ending in the play's score (the word itself renders as game tiles).
   await expect(page.getByText('Scrabble', { exact: true })).toBeVisible();