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.ts

@@ -5,6 +5,8 @@ export { Ack } from './scrabblefb/ack.js';
 export { AlphabetEntry } from './scrabblefb/alphabet-entry.js';
 export { BannerCampaign } from './scrabblefb/banner-campaign.js';
 export { BannerInfo } from './scrabblefb/banner-info.js';
+export { BestMoveTile } from './scrabblefb/best-move-tile.js';
+export { BestMoveView } from './scrabblefb/best-move-view.js';
 export { BlockList } from './scrabblefb/block-list.js';
 export { BlockStatus } from './scrabblefb/block-status.js';
 export { ChatList } from './scrabblefb/chat-list.js';