OIDC providers like Synapse expect the JWT issuer claim to match the
discovery document's issuer URL. Changed JWT plugin config from
JWT_ISSUER to BASE_URL to ensure consistency.
Also adds:
- @manacore/credit-operations package with operation definitions
- @manacore/shared-credit-ui package with React Native and Svelte components
- CreditInterceptor and @UseCredits decorator in nestjs-integration
- Credit system integration in chat backend
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