Agent response schemas missing submissionId in OpenAPI documentation

[astrobot-houston]

Originally reported by @nyxst4ck in #308.

All community-submitted pull requests are automatically converted to issues (bugs) & discussions (feature requests, enhancements) where they can be triaged and prioritized. Once prioritized, a PR implementation is created automatically.

Describe the Bug

The submissionId field is returned at runtime in both agent admission (HTTP 202) and synchronous invocation (HTTP 200) responses, but it is missing from AgentAdmissionResponseSchema and AgentInvocationResponseSchema in packages/runtime/src/runtime/schemas.ts. Because the generated OpenAPI documentation is derived from these Valibot schemas, submissionId is omitted from the published API spec, making it invisible to consumers relying on the documented contract.

Expected Behavior

The OpenAPI specification generated for agent endpoints should include submissionId as a required string field in both the 202 admission response and the 200 synchronous invocation response, matching what the runtime actually returns.

Steps to Reproduce

1. Start a Flue project with at least one agent defined.
2. Inspect the generated OpenAPI spec (e.g. via the /openapi.json endpoint or build output).
3. Look at the response schemas for POST /agents/{name}/{id} — the 202 and 200 response bodies list streamUrl and offset but not submissionId.
4. Send an actual request to the agent endpoint and observe that the runtime response includes a submissionId field not present in the documented schema.

---

Original implementation from #308 by @nyxst4ck