feat(aws): resolve endpoints by service

[aryasaatvik]

Summary

Route individual AWS SDK services to distinct endpoints while preserving the existing operation-scoped Endpoint override and generated Smithy endpoint fallback.

API

Effect.provideService(Endpoint.ServiceEndpoint, {
  resolve: (service) =>
    service === "S3" ? "http://127.0.0.1:9000" : undefined,
});

The resolver receives the model's SDK service ID, so services that share a SigV4 name, such as SES and SESv2, remain independently routable.

Resolution order

Priority	Source	Behavior
1	Endpoint	Explicit operation-scoped override
2	ServiceEndpoint	Service-specific resolver
3	Smithy rules / default	Existing AWS endpoint selection

The same resolution path is used by generated operations and S3 presigning.

Validation

• mise exec bun@1.3.13 -- bun test packages/aws/test/endpoint.test.ts — 7 passing tests
• oxfmt --check on the four changed files