fix(cli): install git hooks from the repository root only

[blafourcade]

🎯 What & why

A stray cli/lefthook.yml holding lefthook's example config kept appearing untracked in linked worktrees (#860). Worse, whatever wrote it also reinstalled the git hooks that every worktree shares.

🛠️ How it works

The chain, reproduced in throwaway repos with lefthook 2.1.12 and pnpm 12.3.4:

1. In a linked worktree, git exports GIT_DIR into every hook; the main checkout gets only GIT_INDEX_FILE.
2. A pre-commit or pre-push job runs pnpm inside cli/ (cd cli && pnpm lint, pnpm test:arch, pnpm typecheck, pnpm --dir cli knip, pnpm --dir cli test). When cli/node_modules is missing or stale, pnpm 12 installs first and runs cli/package.json's "prepare": "lefthook install".
3. With GIT_DIR set and no GIT_WORK_TREE, git takes cli/ for the work tree root. lefthook finds no config there, writes its example, and installs hooks into the shared hooks directory.

The fix:

• cli/package.json drops prepare and its lefthook devDependency. The root package's prepare already installs the hooks, and the Makefile does too, from the root. Nothing else in cli used lefthook: knip flagged the dependency once the script was gone. The lockfile loses the lefthook entries.
• cli/tests/architecture/hooks-install-from-the-root.arch.test.ts asserts that no script of this package calls lefthook. It lives in architecture because that project runs in pre-commit on any cli/** change, so it catches the exact edit that would bring the bug back.

🧪 How to verify

• Red first: the test failed on the old package.json (prepare: lefthook install); green after.
• In the repro: cd cli && GIT_DIR=<root>/.git lefthook install gives Added config: .../cli/lefthook.yml. Without GIT_DIR there is no file. The pre-commit job cd cli && pnpm lint in a linked worktree creates it. With cli's prepare removed, it does not.
• Architecture 25 files, 131 tests; typecheck, lint and knip green. This commit and push, made from a linked worktree, left no cli/lefthook.yml.

⚠️ Heads-up

• Someone who runs pnpm install only inside cli/ no longer gets hooks installed; scripts/doctor.sh already warns when they are missing. Installing from the root is the supported path.
• || true would not have helped: the file still appears with it. A .gitignore entry would only hide it while the shared hooks keep being reinstalled.
• cli/package.json is a harness file, so CI runs every mutation scope.

🔗 Linked issue

Closes #860

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🤖 Generated with Claude Code

https://claude.ai/code/session_011x4ms5qcGuZgYhCxfdHMUb