feat(enakgame): spin as an EnakGame game; remove the old game flow

EnakGame phase 10 of docs/tasks-enakgame.md (EG-1001 to EG-1003).

Spin (EG-1001)
- PROBABILITY entries take an optional label (a wheel segment). The customer game
  list shows a PROBABILITY game's prizes (entry, label, amount, never weights), and
  completing returns the drawn prize, so the client can draw the wheel and stop it
  on the server's draw.
- docs/enakgame-spin.md: the admin steps to set up spin per organization (no
  seeder) and the customer app flow. An HTTP test plays it end to end.

Old game flow removed (EG-1002)
- Routes POST /customer/spin, GET /customer/games, GET /customer/ferris-wheel, and
  admin /marketing/games, /marketing/game-prizes, /marketing/rewards, with their
  handlers, services, processors, repositories, validators, models, contracts,
  mappers and tests (GamePlayProcessor, SpinGameService, rewards, ...). This also
  closes RFC §15 findings 1 and 2 (double charge, spinning another org's game).
- Tables games, game_prizes, game_plays and rewards stay for ledger history.
  entities.StringSlice moves to its own file; the omset tracker (unrouted) keeps
  game_id but no longer embeds the old game response.

games.is_active dropped (EG-1003)
- Migration 000115; nothing reads metadata.coin_cost any more.

The EnakPoint integration docs now point at /customer/enakgame. The Postgres tests
were not run: no test database here. Migration 000115 has not been run anywhere.
The customer app must stop calling the removed endpoints before this is deployed.

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

internal/constants/error.go

@@ -53,15 +53,10 @@ const (
 	// Gamification entities
 	CustomerPointsEntity            = "customer_points"
 	TierEntity                      = "tier"
-	GameEntity                      = "game"
-	GamePrizeEntity                 = "game_prize"
-	GamePlayEntity                  = "game_play"
 	OmsetTrackerEntity              = "omset_tracker"
-	RewardEntity                    = "reward"
 	CampaignEntity                  = "campaign"
 	CampaignRuleEntity              = "campaign_rule"
 	CustomerEntity                  = "customer"
-	SpinGameHandlerEntity           = "spin_game_handler"
 	UserDeviceServiceEntity         = "user_device_service"
 	NotificationServiceEntity       = "notification_service"
 	NotificationHandlerEntity       = "notification_handler"