test: add hello-world MCP golden path

[JaylanJerry]

Summary

• Add tests/e2e/golden-path.test.ts as the proof that the MCP loop still works end to end.
• Drive an empty git repo through permission, failed verify, continue, review, approve, apply, and worktree cleanup.
• Assert main does not move before apply, the checkpoint parent is the base commit, and leftover worktrees are gone.

Test plan

• npm test -- tests/e2e/golden-path.test.ts
• Confirm approve-before-apply leaves the project HEAD unchanged
• Confirm apply lands hello.js / hello.test.js and removes the worktree
• Merge only after docs: make first-run install and doctor usable #11

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