feat(supervisor): push gateway desired state - #2967

Summary

Implement issue #1731 in one PR. Replace supervisor polling for gateway-owned desired state with bootstrap and correlated ConfigUpdate snapshots over ConnectSupervisor.

This PR is a draft while the protocol, startup ordering, update application, reconciliation, polling removal, tests, and documentation are completed.

Related Issue

Closes #1731

Planned Changes

• Rename the existing config, provider-environment, and inference response messages as reusable snapshot types.
• Carry a complete bootstrap in SessionAccepted and gate initialization on its result.
• Deliver later component snapshots through correlated, sequenced ConfigUpdate messages.
• Add bounded owner reconciliation and immediate invalidation.
• Preserve standalone and local-override behavior.
• Remove obsolete supervisor polling and internal provider/inference fetch RPCs.
• Update architecture and compatibility documentation.

Excluded

Changing deployment defaults for supervisor:latest is not part of this PR.

Testing

Work in progress. Final verification will include focused protocol/runtime tests, mise run pre-commit, mise run test, relevant sandbox E2E coverage, and mise run ci.

Checklist

• Implementation complete
• Documentation updated
• Pre-commit passes
• Unit and integration tests pass
• Relevant E2E coverage passes
• Full CI passes