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.

pkg/fbs/scrabble.fbs

@@ -497,6 +497,10 @@ table StatsView {
   max_game_points:int;
   max_word_points:int;
   best_moves:[BestMoveView];
+  // moves is the player's lifetime play count (tile placements); hints_used is their lifetime
+  // hint count. The screen shows the hint share = hints_used / moves (added trailing).
+  moves:int;
+  hints_used:int;
 }
 
 // TargetRequest names a single counterpart account (friend request/cancel/unfriend,

pkg/fbs/scrabblefb/StatsView.go

@@ -121,8 +121,32 @@ func (rcv *StatsView) BestMovesLength() int {
 	return 0
 }
 
+func (rcv *StatsView) Moves() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(16))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *StatsView) MutateMoves(n int32) bool {
+	return rcv._tab.MutateInt32Slot(16, n)
+}
+
+func (rcv *StatsView) HintsUsed() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(18))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *StatsView) MutateHintsUsed(n int32) bool {
+	return rcv._tab.MutateInt32Slot(18, n)
+}
+
 func StatsViewStart(builder *flatbuffers.Builder) {
-	builder.StartObject(6)
+	builder.StartObject(8)
 }
 func StatsViewAddWins(builder *flatbuffers.Builder, wins int32) {
 	builder.PrependInt32Slot(0, wins, 0)
@@ -145,6 +169,12 @@ func StatsViewAddBestMoves(builder *flatbuffers.Builder, bestMoves flatbuffers.U
 func StatsViewStartBestMovesVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
 	return builder.StartVector(4, numElems, 4)
 }
+func StatsViewAddMoves(builder *flatbuffers.Builder, moves int32) {
+	builder.PrependInt32Slot(6, moves, 0)
+}
+func StatsViewAddHintsUsed(builder *flatbuffers.Builder, hintsUsed int32) {
+	builder.PrependInt32Slot(7, hintsUsed, 0)
+}
 func StatsViewEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }