fix: warn when fd is missing outside git repos

[Eric-Song-Nop]

Related Issue

Related to #266

Problem

When fd is not installed, @ file completion still works inside git repositories through the existing git fallback, but outside git repositories it may not return candidates. That failure mode was not visible to users.

该项目并没有明确fd应该是一个系统依赖。

What changed

这是一个最小警告，我在系统中没有fd且不在git项目中启动kimi code是进行了最小化警报。

The TUI now shows a startup warning only when fd is missing and the current directory is not a git repository. Git repositories stay quiet because the existing git ls-files fallback remains available.

Added startup tests covering missing fd in git and non-git directories, plus the fd-available path.

Validation:

• corepack pnpm exec vitest run apps/kimi-code/test/tui/kimi-tui-startup.test.ts apps/kimi-code/test/tui/components/editor/file-mention-provider.test.ts apps/kimi-code/test/utils/git/git-ls-files.test.ts
• corepack pnpm --filter @moonshot-ai/kimi-code run typecheck
• corepack pnpm exec oxlint --type-aware apps/kimi-code/src/tui/kimi-tui.ts apps/kimi-code/test/tui/kimi-tui-startup.test.ts
• git diff --check

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: e0114d4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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[Eric-Song-Nop]

@liruifengv 实际上真正在pi agent中的做法是，https://github.com/earendil-works/pi/blob/335e09ba0d12ddb3f169ca323df0bef0fd61cc48/packages/coding-agent/src/utils/tools-manager.ts#L326 保证了 fd和rg的安装，我并没有检查rg是否在kimi code中也是必须的，但是我认为kimi code应该用同样的机制保证他们的安装。可以开新的pr或者继续在这个pr上添加。