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/lib/hints.ts

@@ -0,0 +1,26 @@
+// Hint-count derivation, kept out of the .svelte component so it is unit-testable.
+//
+// The badge shows the per-game hint allowance remaining plus the player's global hint
+// wallet. The server's hints_remaining folds the two together, but the wallet is global —
+// shared across every game — so caching the combined number per game makes it go stale the
+// moment a wallet hint is spent in another game. We therefore split it: the per-game
+// allowance is hints_remaining - wallet_balance (both from the same fetch, so it is stable
+// and cacheable), and the wallet is read live from the global profile, never the per-game
+// snapshot.
+
+import type { StateView } from './model';
+
+/**
+ * hintsLeft is the hint count for the badge: the per-game allowance remaining (the view's
+ * hints_remaining minus the wallet snapshot baked into that same view) plus the live global
+ * wallet balance. Passing the live wallet (not view.walletBalance) is what keeps the count
+ * correct when a wallet hint was spent in another game since this view was fetched.
+ */
+export function hintsLeft(
+  view: Pick<StateView, 'hintsRemaining' | 'walletBalance'> | null,
+  walletBalance: number,
+): number {
+  if (!view) return 0;
+  const allowance = Math.max(0, view.hintsRemaining - view.walletBalance);
+  return allowance + Math.max(0, walletBalance);
+}