feat: add Kimi Code plugin adapter

[Phoen1xCode]

What

Adds a Kimi Code adapter so the repo installs directly as a Kimi Code plugin:

/plugins install https://github.com/DietrichGebert/ponytail

(or /plugins → Custom tab → paste the repo URL, then /reload)

How

A self-contained plugin dir, .kimi-plugin/ (a manifest location Kimi Code recognizes, mirroring .qoder-plugin/ and friends), wiring the repo's shared files plus its own command copies:

Manifest field	Points at	Effect
skills	./skills/	the six ponytail skills
commands	./.kimi-plugin/commands/	dedicated Markdown command copies, registered as /ponytail:ponytail, /ponytail:ponytail-review, …
systemPromptPath	./AGENTS.md	compact ruleset in the system prompt every session (2.6 KB, well under the 32 KB cap)
sessionStart.skill	ponytail	full skill loaded at every session start

The command files are Kimi-specific copies rather than pointers at .opencode/command/, so the two adapters evolve independently; tests/commands.test.js pins one file per registered command and tests/kimi-plugin.test.js byte-compares the two sets, so a one-sided edit fails loudly instead of drifting.

Also: scripts/check-versions.js now pins .kimi-plugin/plugin.json with the other eight version files, plus README (Install / Commands / Uninstall) and docs/agent-portability.md entries.

Why no hooks

Ponytail's lifecycle hooks emit per-host output shapes hardcoded for Claude/Codex/Copilot/Qoder (hooks/ponytail-runtime.js). Kimi Code's hook protocol (stdin payload, stdout contract) doesn't match any of them, so declaring the existing scripts would append Claude-shaped JSON verbatim to the user's context. The system-prompt contribution plus the session-start skill already cover always-on behavior; the trade-off is that /ponytail:ponytail ultra level switches live for the session instead of persisting via the flag file.

Test plan

• tests/kimi-plugin.test.js (new, 9 tests):
  • manifest exists with valid plugin id and pinned version aligned with the other manifests
  • only spec-supported fields
  • every referenced ./ path stays inside the plugin root and exists
  • systemPromptPath carries the rule invariants within the 32 KB budget
  • sessionStart.skill resolves to a shipped skill
  • all six skills present
  • every pi-registered command resolves to a parseable Markdown command in the declared dir
  • the Kimi and OpenCode command sets stay byte-identical
• tests/commands.test.js: every registered command now also needs a .kimi-plugin/commands/*.md file.
• npm test - 118 tests pass (incl. the new ones). Note: the csv correctness test needs pandas installed locally, as documented in the README.
• node scripts/check-rule-copies.js and node scripts/check-versions.js pass.