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.

pkg/fbs/scrabble.fbs

@@ -240,6 +240,12 @@ table StateView {
   bag_len:int;
   hints_remaining:int;
   alphabet:[AlphabetEntry];
+  // wallet_balance is the requesting player's global hint-wallet balance, sent apart from
+  // hints_remaining (which folds the wallet in with the per-game allowance) so the client can
+  // separate the two: the per-game allowance remaining is hints_remaining - wallet_balance, and
+  // the wallet is a single global figure the client keeps live across games (added trailing —
+  // backward-compatible).
+  wallet_balance:int;
 }
 
 // GameActionRequest carries just a game id (pass / resign / hint / history).
@@ -290,10 +296,14 @@ table ComplaintRequest {
   note:string;
 }
 
-// HintResult is the top-ranked move plus the remaining hint budget.
+// HintResult is the top-ranked move plus the remaining hint budget. wallet_balance is the
+// global hint-wallet balance after spending (see StateView.wallet_balance), so the client
+// refreshes its live wallet and re-derives the per-game allowance (added trailing —
+// backward-compatible).
 table HintResult {
   move:MoveRecord;
   hints_remaining:int;
+  wallet_balance:int;
 }
 
 // DraftRequest saves the player's client-side composition for a game: a single
@@ -458,14 +468,39 @@ table LinkResult {
   session:Session;
 }
 
+// BestMoveTile is one letter cell of a best-move word: its concrete letter (the designated
+// letter for a blank), its tile point value (0 for a blank) and whether it is a blank. It
+// lets the client render the word as game tiles without the variant's alphabet table.
+table BestMoveTile {
+  letter:string;
+  value:int;
+  blank:bool;
+}
+
+// BestMoveView is an account's highest-scoring single play within one game variant: the
+// variant label, the play's total score (matching max_word_points for that variant) and its
+// main word as ordered tiles.
+table BestMoveView {
+  variant:string;
+  score:int;
+  word:[BestMoveTile];
+}
+
 // StatsView is a durable account's lifetime statistics (games-played and win-rate
-// are derived client-side).
+// are derived client-side). best_moves breaks the best move down per variant, carrying the
+// word itself; it is empty for an account with no recorded play and lists only variants the
+// account has played (added trailing — backward-compatible).
 table StatsView {
   wins:int;
   losses:int;
   draws:int;
   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,