Add Kimi Code CLI as a built-in engine

[mrryf]

Refs #218

Summary

Adds the Kimi Code CLI as a built-in Agon engine using engine ID kimi-code via engines/kimi-code.json.

The engine uses the same non-interactive CLI route for exec and agent dispatch:

kimi --output-format text -p <prompt>

The explicit kimi-code ID keeps this integration scoped to the Kimi Code CLI and avoids ambiguity with other Kimi/Moonshot integrations.

Changes

• Add built-in kimi-code engine definition.
• Document Kimi Code in the README engine list.
• Add coverage for dispatch args, engine activation, doctor/config behavior, health checks, and orchestration filtering.
• Keep the engine definition free of permissive approval flags such as --auto, -y, and --yolo.

Verification

• npm run kern:compile
• npm run build
• npm run typecheck
• git diff --check
• Targeted Kimi Code unit/integration tests
• Live Agon smoke through kimi-code: passed in a disposable /private/tmp git repo, changing one file from status=red to status=green; recorded diffLines: 2, filesChanged: 1.

Note: the full local suite reproduced four existing local/baseline failures unrelated to this integration.