feat(guardrails): パターンL–Oのテスト検証信頼性ガードを追加

[terisuke]

Summary

• Issue feat(guardrails): patterns L-O — test verification gaps beyond A-K (env-dependent skips, worktree env, runner API limits, env-var instability) #290: A–K では見えないテスト検証の抜け穴（L–O）を実測ベースでガード化
• いずれも 助言 + skill/command + 結線ヘルパー（ハードブロックなし = パターン I）

パターン

#	内容	手段
L	SKIP 黙認を green と誤認	test-honesty.ts + /test-honesty
M	worktree に node_modules 無し	worktree-bootstrap.ts
N	fireEvent 等で vacuous pass	skill harness-api-gotcha + falsifiable-change
O	ambient env でテストが分岐	env-hermetic.ts + skill env-hermetic-tests

受入（I）

• 陰性: skip=0 / node_modules あり / vi.mock 済み → 助言なし
• 陽性: DB skip / 欠如 node_modules / gate のみ → 助言
• 反証: OPENCODE_*_GUARD=off で助言消える

Test plan

• bun test test/plugin/test-reliability-guards.test.ts（17 pass）
• local:deploy / local:check green
• ライブ: L advisory / O violation+hermetic
• CI green 後マージ

Closes #290

Made with Cursor

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

The following comment was made by an LLM, it may be inaccurate: