fix(tgit): run gf auth commands from a neutral cwd

[jeff-r2026]

Problem

teamai init fails with gf auth login failed when run inside a git repository whose origin remote is not git.woa.com (e.g. a GitHub mirror — including this very repo).

Root cause: gf auth whoami / gf auth login inspect the current git repository's origin remote and scope the authentication check to that remote's host. When teamai runs from a repo whose origin is github.com, gf reports "还未登录" (not logged in) even though a valid git.woa.com OAuth token exists. ensureAuthenticated() takes that at face value, re-triggers interactive login, and fails.

The token itself is valid — the check is just being run from the wrong place. Reproduced deterministically:

cwd	gf auth whoami
a repo with origin = git.woa.com/...	✅ 当前登录用户
a repo with origin = github.com/...	❌ 还未登录
a non-git dir (/tmp)	✅ 当前登录用户

Fix

Run the three gf auth calls (gfIsAuthenticated, gfAuthWhoami, gfAuthLogin) from a neutral working directory (os.tmpdir(), which is not a git repo). Authentication is host-scoped (git.woa.com), so it must not depend on the cwd's local git remote.

Test Plan

• npm run build — success
• npx vitest run src/__tests__/gf-cli.test.ts — 13 passed (added 3 tests asserting each auth call spawns with cwd = os.tmpdir())
• npx tsc --noEmit on changed files — no errors
• End-to-end: ran the built CLI's teamai init from a temp repo whose origin = github.com/Tencent/teamai-cli (the failing condition) → ✔ Authenticated as jeffyxu, no interactive login triggered, clone + config + hooks all completed.

Note: 9 pre-existing failures in iwiki-dual / iwiki-review-apply / import-repo-incremental are unrelated (local vitest version drift) and reproduce on a pristine main checkout without this change.

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