Add credits.ts to @manacore/shared-hono as replacement for
CreditClientService from @mana-core/nestjs-integration.
Exports: getBalance, validateCredits, consumeCredits, refundCredits
Calls mana-credits service via MANA_CREDITS_URL + X-Service-Key.
Same API surface as the NestJS version but as pure functions
instead of an @Injectable() service class.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
