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/models/enakgame.go

@@ -199,6 +199,34 @@ type GameSessionListQuery struct {
 	Limit  int    `form:"limit"`
 }
 
+// EnakGameLeaderboardQuery picks a week of the leaderboard, and optionally one game.
+type EnakGameLeaderboardQuery struct {
+	// Any day of the week, YYYY-MM-DD in Asia/Jakarta; this week when empty.
+	Date   string `form:"date"`
+	GameID string `form:"game_id"`
+	Limit  int    `form:"limit"`
+}
+
+// EnakGameLeaderboard ranks the customers of an organization by the EnakCoin they won
+// from games in one week, Monday to Sunday in Asia/Jakarta.
+type EnakGameLeaderboard struct {
+	WeekStart string                     `json:"week_start"`
+	WeekEnd   string                     `json:"week_end"`
+	GameID    *uuid.UUID                 `json:"game_id"`
+	Entries   []EnakGameLeaderboardEntry `json:"entries"`
+	// The customer asking, wherever they rank; null when they won nothing that week.
+	Me *EnakGameLeaderboardEntry `json:"me"`
+}
+
+// EnakGameLeaderboardEntry is one customer on the leaderboard. Other customers are
+// shown by a masked name only.
+type EnakGameLeaderboardEntry struct {
+	Rank  int    `json:"rank"`
+	Name  string `json:"name"`
+	Coins int64  `json:"coins"`
+	IsMe  bool   `json:"is_me"`
+}
+
 // GameSessionCompleteInput is what the client reports at the end of a play (§7.2): data
 // only. Anything else it sends, a reward amount above all, is ignored (P1).
 type GameSessionCompleteInput struct {