feat(stats): best-move word, moves & hint-share, and a hint-count fix (#81)

The statistics screen gains real depth, plus a hint-count bug fix found along the way.

- Best move per variant: the screen shows the actual best-move word (drawn as game
  tiles; a wildcard shows its letter but no value), broken down by game variant, empty
  variants omitted. New account_best_move table, written at game finish.
- Moves & hint share: two new lifetime tiles — the player's play count and the share of
  plays that used a hint — from summed account_stats counters (moves, hints_used).
  Honest-AI games are excluded, like the rest of the stats.
- Hint-count fix: the in-game hint badge no longer goes stale across games. The global
  wallet now rides the wire apart from the per-game allowance (wallet_balance on
  StateView/HintResult/StatsView), so the client reads the live wallet rather than a
  per-game snapshot; game_players.hints_used now counts every hint (allowance + wallet),
  its true per-game total.
- Account merge: sums the new moves/hints_used counters and merges the per-variant best
  moves (higher score kept), which it previously dropped.
- Admin: the user card shows Moves and Hints used.
- UI polish: tab/label wording, game-over text, and e2e selectors hardened against label
  changes.

All wire additions are trailing (backward-compatible). Docs (ARCHITECTURE, FUNCTIONAL +ru,
UISN_DESIGN) updated in step.

ui/src/gen/fbs/scrabblefb/hint-result.ts

@@ -33,8 +33,13 @@ hintsRemaining():number {
   return offset ? this.bb!.readInt32(this.bb_pos + offset) : 0;
 }
 
+walletBalance():number {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.readInt32(this.bb_pos + offset) : 0;
+}
+
 static startHintResult(builder:flatbuffers.Builder) {
-  builder.startObject(2);
+  builder.startObject(3);
 }
 
 static addMove(builder:flatbuffers.Builder, moveOffset:flatbuffers.Offset) {
@@ -45,15 +50,20 @@ static addHintsRemaining(builder:flatbuffers.Builder, hintsRemaining:number) {
   builder.addFieldInt32(1, hintsRemaining, 0);
 }
 
+static addWalletBalance(builder:flatbuffers.Builder, walletBalance:number) {
+  builder.addFieldInt32(2, walletBalance, 0);
+}
+
 static endHintResult(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createHintResult(builder:flatbuffers.Builder, moveOffset:flatbuffers.Offset, hintsRemaining:number):flatbuffers.Offset {
+static createHintResult(builder:flatbuffers.Builder, moveOffset:flatbuffers.Offset, hintsRemaining:number, walletBalance:number):flatbuffers.Offset {
   HintResult.startHintResult(builder);
   HintResult.addMove(builder, moveOffset);
   HintResult.addHintsRemaining(builder, hintsRemaining);
+  HintResult.addWalletBalance(builder, walletBalance);
   return HintResult.endHintResult(builder);
 }
 }