[codex] Make declarative handlers schema-aware

[k-kinzal]

Summary

• Defer server subclass declarative handler registration until the OpenAPI schema is resolved in buildInterceptor().
• Register method-name operation handlers only when the operationId exists in the schema.
• Register #[Route] handlers only when the schema contains the matching path/method.
• Keep explicit fluent handlers separate by cloning the explicit handler map before adding schema-aware declarative handlers.

Validation

• composer test
• composer lint