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/server/handlers_account.go

@@ -38,6 +38,8 @@ type statsDTO struct {
 	Draws         int           `json:"draws"`
 	MaxGamePoints int           `json:"max_game_points"`
 	MaxWordPoints int           `json:"max_word_points"`
+	Moves         int           `json:"moves"`
+	HintsUsed     int           `json:"hints_used"`
 	BestMoves     []bestMoveDTO `json:"best_moves,omitempty"`
 }
 
@@ -165,6 +167,8 @@ func (s *Server) handleStats(c *gin.Context) {
 		Draws:         st.Draws,
 		MaxGamePoints: st.MaxGamePoints,
 		MaxWordPoints: st.MaxWordPoints,
+		Moves:         st.Moves,
+		HintsUsed:     st.HintsUsed,
 		BestMoves:     best,
 	})
 }