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.

backend/internal/game/store.go

@@ -66,6 +66,8 @@ type statDelta struct {
 	draws       int
 	gamePoints  int
 	wordPoints  int
+	moves       int // plays this game (tile placements), summed into account_stats.moves
+	hintsUsed   int // hints used this game (allowance + wallet), summed into account_stats.hints_used
 	bestVariant string
 	bestScore   int
 	bestTiles   []account.BestMoveTile
@@ -729,13 +731,17 @@ func upsertStats(ctx context.Context, tx *sql.Tx, d statDelta, now time.Time) er
 	draws := row.Draws + int32(d.draws)
 	maxGame := max(row.MaxGamePoints, int32(d.gamePoints))
 	maxWord := max(row.MaxWordPoints, int32(d.wordPoints))
+	moves := row.Moves + int32(d.moves)
+	hintsUsed := row.HintsUsed + int32(d.hintsUsed)
 
 	upd := table.AccountStats.UPDATE(
 		table.AccountStats.Wins, table.AccountStats.Losses, table.AccountStats.Draws,
 		table.AccountStats.MaxGamePoints, table.AccountStats.MaxWordPoints, table.AccountStats.UpdatedAt,
+		table.AccountStats.Moves, table.AccountStats.HintsUsed,
 	).SET(
 		postgres.Int(int64(wins)), postgres.Int(int64(losses)), postgres.Int(int64(draws)),
 		postgres.Int(int64(maxGame)), postgres.Int(int64(maxWord)), postgres.TimestampzT(now),
+		postgres.Int(int64(moves)), postgres.Int(int64(hintsUsed)),
 	).WHERE(table.AccountStats.AccountID.EQ(postgres.UUID(d.accountID)))
 	if _, err := upd.ExecContext(ctx, tx); err != nil {
 		return fmt.Errorf("update stats %s: %w", d.accountID, err)
@@ -774,8 +780,10 @@ func upsertBestMove(ctx context.Context, tx *sql.Tx, d statDelta, now time.Time)
 	return nil
 }
 
-// SpendHintAllowance increments a seat's per-game hint counter by one.
-func (s *Store) SpendHintAllowance(ctx context.Context, gameID uuid.UUID, seat int) error {
+// IncHintsUsed increments a seat's per-game hints-used counter by one. It is called for
+// every hint — both the free per-game allowance and the wallet-charged ones — so the counter
+// is the seat's total hints used this game (the first HintsPerPlayer being the allowance).
+func (s *Store) IncHintsUsed(ctx context.Context, gameID uuid.UUID, seat int) error {
 	stmt := table.GamePlayers.
 		UPDATE(table.GamePlayers.HintsUsed).
 		SET(table.GamePlayers.HintsUsed.ADD(postgres.Int(1))).
@@ -784,7 +792,7 @@ func (s *Store) SpendHintAllowance(ctx context.Context, gameID uuid.UUID, seat i
 				AND(table.GamePlayers.Seat.EQ(postgres.Int(int64(seat)))),
 		)
 	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
-		return fmt.Errorf("game: spend hint allowance: %w", err)
+		return fmt.Errorf("game: increment hints used: %w", err)
 	}
 	return nil
 }