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.

gateway/internal/transcode/transcode_social_test.go

@@ -195,6 +195,7 @@ func TestStatsRoundTrip(t *testing.T) {
 			t.Errorf("unexpected path %q", r.URL.Path)
 		}
 		_, _ = w.Write([]byte(`{"wins":5,"losses":3,"draws":1,"max_game_points":420,"max_word_points":90,` +
+			`"moves":248,"hints_used":12,` +
 			`"best_moves":[{"variant":"scrabble_en","score":90,"word":[` +
 			`{"letter":"c","value":3,"blank":false},` +
 			`{"letter":"a","value":0,"blank":true},` +
@@ -212,6 +213,9 @@ func TestStatsRoundTrip(t *testing.T) {
 	if st.Wins() != 5 || st.Losses() != 3 || st.Draws() != 1 || st.MaxGamePoints() != 420 || st.MaxWordPoints() != 90 {
 		t.Fatalf("stats decoded wrong: %+v", st)
 	}
+	if st.Moves() != 248 || st.HintsUsed() != 12 {
+		t.Fatalf("moves/hints decoded wrong: moves=%d hints=%d", st.Moves(), st.HintsUsed())
+	}
 	if st.BestMovesLength() != 1 {
 		t.Fatalf("best moves length = %d, want 1", st.BestMovesLength())
 	}