fix(api): inject langgraph_auth_user on protocol-v2 run.start (#2590)

## Summary
- Inject `langgraph_auth_user`, `langgraph_auth_user_id`, and
`langgraph_auth_permissions` into run config in protocol v2
`createOrResumeRun`, matching the REST `createValidRun` behavior.
- Extract shared `applyAuthToRunConfig` /
`applyRequestHeadersToRunConfig` helpers and use them from both REST and
protocol paths.
- Pass `userId` into `runs.put()` from the protocol path for parity with
REST.