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/entities/string_slice.go

@@ -0,0 +1,38 @@
+package entities
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+)
+
+// StringSlice is a custom type for []string that implements sql.Scanner and driver.Valuer
+type StringSlice []string
+
+// Scan implements the sql.Scanner interface for StringSlice
+func (s *StringSlice) Scan(value interface{}) error {
+	if value == nil {
+		*s = StringSlice{}
+		return nil
+	}
+
+	var bytes []byte
+	switch v := value.(type) {
+	case []byte:
+		bytes = v
+	case string:
+		bytes = []byte(v)
+	default:
+		return fmt.Errorf("cannot scan %T into StringSlice", value)
+	}
+
+	return json.Unmarshal(bytes, s)
+}
+
+// Value implements the driver.Valuer interface for StringSlice
+func (s StringSlice) Value() (driver.Value, error) {
+	if s == nil {
+		return nil, nil
+	}
+	return json.Marshal(s)
+}