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.

backend/internal/accountmerge/merge.go

@@ -1,5 +1,6 @@
 // Package accountmerge retires a secondary account into a primary one in a single
-// transaction: it sums statistics and the hint wallet, ORs the paid flag, repoints
+// transaction: it sums statistics (merging the per-variant best moves), sums the hint
+// wallet, ORs the paid flag, repoints
 // the secondary's identities, transfers its games/chat/complaints/invitations,
 // de-duplicates friends and blocks, and leaves the secondary as an audit tombstone
 // (accounts.merged_into). It is the data core of account linking & merge
@@ -68,6 +69,9 @@ func (m *Merger) Merge(ctx context.Context, primary, secondary uuid.UUID) error
 		if err := mergeStats(ctx, tx, primary, secondary, now); err != nil {
 			return err
 		}
+		if err := mergeBestMoves(ctx, tx, primary, secondary, now); err != nil {
+			return err
+		}
 		if err := mergeAccountFields(ctx, tx, primary, secondary, now); err != nil {
 			return err
 		}
@@ -147,8 +151,8 @@ func activeGameIDs(ctx context.Context, tx *sql.Tx, accountID uuid.UUID) ([]uuid
 	return out, nil
 }
 
-// mergeStats folds secondary's lifetime statistics into primary (wins/losses/draws
-// summed, max points kept) and deletes the secondary row.
+// mergeStats folds secondary's lifetime statistics into primary (wins/losses/draws and
+// the moves/hints-used counters summed, max points kept) and deletes the secondary row.
 func mergeStats(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, now time.Time) error {
 	var sec model.AccountStats
 	err := postgres.SELECT(table.AccountStats.AllColumns).
@@ -178,13 +182,16 @@ func mergeStats(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, n
 
 	upd := table.AccountStats.UPDATE(
 		table.AccountStats.Wins, table.AccountStats.Losses, table.AccountStats.Draws,
-		table.AccountStats.MaxGamePoints, table.AccountStats.MaxWordPoints, table.AccountStats.UpdatedAt,
+		table.AccountStats.MaxGamePoints, table.AccountStats.MaxWordPoints,
+		table.AccountStats.Moves, table.AccountStats.HintsUsed, table.AccountStats.UpdatedAt,
 	).SET(
 		postgres.Int(int64(pri.Wins+sec.Wins)),
 		postgres.Int(int64(pri.Losses+sec.Losses)),
 		postgres.Int(int64(pri.Draws+sec.Draws)),
 		postgres.Int(int64(max(pri.MaxGamePoints, sec.MaxGamePoints))),
 		postgres.Int(int64(max(pri.MaxWordPoints, sec.MaxWordPoints))),
+		postgres.Int(int64(pri.Moves+sec.Moves)),
+		postgres.Int(int64(pri.HintsUsed+sec.HintsUsed)),
 		postgres.TimestampzT(now),
 	).WHERE(table.AccountStats.AccountID.EQ(postgres.UUID(primary)))
 	if _, err := upd.ExecContext(ctx, tx); err != nil {
@@ -198,6 +205,41 @@ func mergeStats(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, n
 	return nil
 }
 
+// mergeBestMoves folds secondary's per-variant best moves into primary, keeping the
+// higher-scoring play per variant (the same rule the per-game upsert uses), then deletes
+// the secondary's rows — the secondary is only tombstoned, not removed, so without this
+// they would linger on a dead account and never reach the merged statistics screen.
+func mergeBestMoves(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, now time.Time) error {
+	var srows []model.AccountBestMove
+	err := postgres.SELECT(table.AccountBestMove.AllColumns).
+		FROM(table.AccountBestMove).
+		WHERE(table.AccountBestMove.AccountID.EQ(postgres.UUID(secondary))).
+		QueryContext(ctx, tx, &srows)
+	if err != nil && !errors.Is(err, qrm.ErrNoRows) {
+		return fmt.Errorf("accountmerge: load secondary best moves: %w", err)
+	}
+	for _, s := range srows {
+		ins := table.AccountBestMove.
+			INSERT(table.AccountBestMove.AccountID, table.AccountBestMove.Variant,
+				table.AccountBestMove.Score, table.AccountBestMove.Tiles, table.AccountBestMove.UpdatedAt).
+			VALUES(primary, s.Variant, s.Score, s.Tiles, postgres.TimestampzT(now)).
+			ON_CONFLICT(table.AccountBestMove.AccountID, table.AccountBestMove.Variant).
+			DO_UPDATE(postgres.SET(
+				table.AccountBestMove.Score.SET(table.AccountBestMove.EXCLUDED.Score),
+				table.AccountBestMove.Tiles.SET(table.AccountBestMove.EXCLUDED.Tiles),
+				table.AccountBestMove.UpdatedAt.SET(table.AccountBestMove.EXCLUDED.UpdatedAt),
+			).WHERE(table.AccountBestMove.EXCLUDED.Score.GT(table.AccountBestMove.Score)))
+		if _, err := ins.ExecContext(ctx, tx); err != nil {
+			return fmt.Errorf("accountmerge: merge best move %s: %w", s.Variant, err)
+		}
+	}
+	del := table.AccountBestMove.DELETE().WHERE(table.AccountBestMove.AccountID.EQ(postgres.UUID(secondary)))
+	if _, err := del.ExecContext(ctx, tx); err != nil {
+		return fmt.Errorf("accountmerge: delete secondary best moves: %w", err)
+	}
+	return nil
+}
+
 // mergeAccountFields adds secondary's hint wallet to primary and ORs the paid flag;
 // all other profile fields stay the primary's.
 func mergeAccountFields(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, now time.Time) error {