feat(enakgame): weekly leaderboard

GET /customer/enakgame/leaderboard ranks the customers of an organization by
the EnakCoin they won from games in one week, Monday to Sunday in
Asia/Jakarta. Only completed, unflagged sessions count, by the week they
started; entry cost is not subtracted. Equal totals rank by who reached
theirs first, so no two customers share a rank.

Optional date (any day of the week, this week by default), game_id and limit
(10, at most 100). The response holds the top ranks and, under me, the
customer asking wherever they rank. Other customers are shown by a masked
name: the first word whole, the others by their first letter; a word with a
digit keeps only its first character.

The EnakGame web game shows it: integration-enakgame.md §10 (checklist now
§11) and RFC §11. The DB test needs TEST_DATABASE_URL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/repository/game_session_repository.go

@@ -70,6 +70,32 @@ type GameSessionRepository interface {
 
 	CreateSessionRewards(ctx context.Context, rewards []entities.GameSessionReward) error
 	ListSessionRewards(ctx context.Context, sessionID uuid.UUID) ([]entities.GameSessionReward, error)
+
+	// Leaderboard ranks the active customers of an organization by the EnakCoin their
+	// completed, unflagged sessions started in [from, to) won, and returns the first
+	// limit ranks plus the row of filter.CustomerID wherever it ranks.
+	Leaderboard(ctx context.Context, filter LeaderboardFilter) ([]LeaderboardRow, error)
+}
+
+// LeaderboardFilter selects the sessions a leaderboard counts.
+type LeaderboardFilter struct {
+	OrganizationID uuid.UUID
+	// Nil for every game.
+	GameID *uuid.UUID
+	From   time.Time
+	To     time.Time
+	Limit  int
+	// The customer asking, returned even below Limit.
+	CustomerID uuid.UUID
+}
+
+// LeaderboardRow is one customer's total. Equal totals rank by who reached theirs
+// first, so no two rows share a rank.
+type LeaderboardRow struct {
+	Rank       int
+	CustomerID uuid.UUID
+	Name       string
+	Coins      int64
 }
 
 type gameSessionRepository struct {
@@ -255,3 +281,45 @@ func (r *gameSessionRepository) ListDueSessions(ctx context.Context, now time.Ti
 	}
 	return due, nil
 }
+
+func (r *gameSessionRepository) Leaderboard(ctx context.Context, filter LeaderboardFilter) ([]LeaderboardRow, error) {
+	gameFilter, args := "", []any{filter.OrganizationID, filter.From, filter.To, constants.GameSessionStatusCompleted}
+	if filter.GameID != nil {
+		gameFilter = "AND s.game_id = ?"
+		args = append(args, *filter.GameID)
+	}
+	args = append(args, filter.Limit, filter.CustomerID)
+	var rows []struct {
+		Rank       int
+		CustomerID string
+		Name       string
+		Coins      int64
+	}
+	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
+		WITH totals AS (
+			SELECT s.customer_id, SUM(s.reward_total) AS coins, MAX(s.ended_at) AS reached_at
+			FROM game_sessions s
+			WHERE s.organization_id = ? AND s.started_at >= ? AND s.started_at < ?
+				AND s.status = ? AND NOT s.flagged AND s.reward_total > 0 `+gameFilter+`
+			GROUP BY s.customer_id
+		), ranked AS (
+			SELECT t.customer_id, c.name, t.coins,
+				ROW_NUMBER() OVER (ORDER BY t.coins DESC, t.reached_at, t.customer_id) AS rank
+			FROM totals t
+			JOIN customers c ON c.id = t.customer_id AND c.is_active
+		)
+		SELECT rank, customer_id::text AS customer_id, name, coins
+		FROM ranked
+		WHERE rank <= ? OR customer_id = ?
+		ORDER BY rank`, args...).Scan(&rows).Error
+	if err != nil {
+		return nil, fmt.Errorf("failed to read game leaderboard: %w", err)
+	}
+	out := make([]LeaderboardRow, 0, len(rows))
+	for _, row := range rows {
+		l := LeaderboardRow{Rank: row.Rank, Name: row.Name, Coins: row.Coins}
+		l.CustomerID, _ = uuid.Parse(row.CustomerID)
+		out = append(out, l)
+	}
+	return out, nil
+}