feat: add support for Kimi Code hooks and plugin manifest

[kennx]

This PR implements full support for Kimi Code hooks and plugin configuration, enabling Ponytail mode tracking, activation, and subagent instructions injection.

Key Changes

• Manifest: Created .kimi-plugin/plugin.json mapping Kimi Code metadata, display properties, and lifecycle hooks (SessionStart, SubagentStart, UserPromptSubmit).
• Runtime: Modified hooks/ponytail-runtime.js to detect Kimi Code environment, resolve configuration directory to ~/.kimi-code, and write raw output to stdout.
• Statusline Nudge: Modified hooks/ponytail-activate.js to skip statusline setup checks when running inside Kimi Code.
• Mode Tracking: Modified hooks/ponytail-mode-tracker.js to read either prompt or user_prompt (Kimi Code snake_case payload format) to track switches.
• Consistency & Testing:
  • Registered .kimi-plugin/plugin.json in version consistency checks (check-versions.js) and tests (gemini-extension.test.js).
  • Added dedicated tests/kimi-plugin.test.js smoke test.
  • Added new test coverage in tests/hooks.test.js simulating Kimi Code session activation, prompt parsing, and subagent hook runs.
• Packaging & Docs: Included .kimi-plugin/ in npm files (package.json) and documented support in docs/agent-portability.md.

Verification

All automated tests run and pass successfully:

npm test