fix(engine): isolate Git diff fixtures from global hooks

[luojiyin1987]

Problem

packages/host/engine/tests/integration/git-diff.test.ts creates temporary Git repositories.

The fixture commits inherit the user's global core.hooksPath.

A global commit-msg hook can reject fixture messages such as init.

This causes the integration test to fail before it reaches readGitDiff.

Reproduction

Set a global hooks path that runs commitlint.

git config --global core.hooksPath ~/.git-hooks

Run:

pnpm exec vitest run packages/host/engine/tests/integration/git-diff.test.ts

The fixture commit fails with subject-empty and type-empty.

The test already disables GPG signing with commit.gpgsign=false.

Root cause

The test does not override core.hooksPath for fixture commits.

Git therefore runs hooks from the user environment.

Fix

In packages/host/engine/tests/integration/git-diff.test.ts, add this config before commit:

'-c',
`core.hooksPath=${join(cwd, '.git', 'hooks')}`,

Use the fixture repository's own .git/hooks directory.

The default hooks there are safe and do not inherit user hooks.

Validation

A minimal temporary repository commits init successfully when this override is set.

The same commit fails without it when the global commitlint hook is active.

[linear-code]

CODE-402