fix(brokerkit): allow private host credentials

[osolmaz]

Summary

Private Hugging Face Spaces could load the approvals frame but block its later API calls.
MLClaw now permits credentialed CORS on the fixed delegated BrokerKit routes so the Space edge can receive its own access cookie.
MLClaw still authorizes every delegated operation only with the short-lived BrokerKit browser session.

What Changed

The trusted runtime now returns the CORS header required by the updated BrokerKit UI.
The runtime pins the published openclaw-brokerkit@0.3.2 package that sends delegated requests through private hosting edges.

• Add Access-Control-Allow-Credentials: true to delegated responses and preflights.
• Preserve the exact opaque Origin: null check and fixed allowed headers/methods.
• Keep cookies insufficient at the MLClaw application authorization boundary.
• Pin openclaw-brokerkit@0.3.2 in every runtime image version source.
• Rebuild the checked-in runtime bundles and update operator documentation.

Testing

The complete local MLClaw quality gate and the final remote CI run pass.
The paired BrokerKit built-UI browser fixture and release workflow also pass.

• 317 tests passed; 2 optional live tests skipped.
• 97.92% statement coverage.
• Typecheck, lint, build, package validation, secret scan, and Slophammer passed.
• BrokerKit cross-browser suite: 56 passed, 4 scoped skips.
• openclaw-brokerkit@0.3.2 was verified from npm after provenance publication.

Risks

Credentialed CORS is limited to the existing delegated route boundary.
The route still requires an unguessable BrokerKit-Session, rejects non-opaque origins, and never treats a host cookie as delegated authority.

Related: osolmaz/brokerkit#60.