refactor(loyalty): remove what is left of tokens

Tokens are EnakCoin and no app uses the token names any more, so their
compatibility layer goes:

- GET /customer/tokens and its handler, service, processor and response
  types.
- total_tokens and tokens_history on GET /customer/wallet; last_updated
  now comes from the most recent row of either currency.
- token_used and tokens_remaining on game and spin responses, and
  sort_by=token_used on the game play list.
- TOKENS as a campaign type and reward type, with the mapping to COINS:
  migration 000092 already renamed the stored values.

The customer_tokens table and its entity stay, as cmd/wallet-migrate still
reads them, and LEGACY_TOKENS stays as the reference of the MIGRATION rows
it wrote. The docs list the removed names and their replacements.

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

internal/constants/error.go

@@ -52,7 +52,6 @@ const (
 	TableEntity                          = "table"
 	// Gamification entities
 	CustomerPointsEntity            = "customer_points"
-	CustomerTokensEntity            = "customer_tokens"
 	TierEntity                      = "tier"
 	GameEntity                      = "game"
 	GamePrizeEntity                 = "game_prize"