feat: expose validated GonkaGate model catalog

[Dankosik]

Summary

• write the validated GonkaGate chat-completions catalog into provider.gonkagate.models
• keep the selected model as the activation default while allowing Kilo/OpenCode /models switching
• update docs and contract tests for the managed catalog behavior

Verification

• npm run typecheck
• npm run test
• npm run format:check
• npm run package:check
• isolated @kilocode/cli@7.2.0 kilo models gonkagate --verbose smoke showed both managed models