fix: Windows snapshot fails with non-ASCII filenames (Chinese, Japanese, etc.)

[yimingll]

Summary

Fix undo/revert not working on Windows when project contains non-ASCII filenames (e.g., Chinese, Japanese, Korean characters).

Problem

On Windows, Bun's $ template literal incorrectly handles variable interpolation, replacing variables with placeholders like ?__bunstr_0 instead of actual values. This causes:

1. git add . to silently fail adding non-ASCII filenames to snapshot
2. git checkout / git ls-tree to fail finding files during revert
3. Undo command only reverts conversation but not code changes

Solution

Replace all $ template calls with Bun.spawn() which correctly passes arguments as an array, bypassing shell interpolation issues.

Also adds unquote() function to decode git octal-escaped non-ASCII filenames in diff output (when core.quotepath=true, which is the default).

Testing

Tested on Windows 11 with Chinese filenames (e.g., 公共函数.cpp) - undo now correctly reverts files.

Fixes #10210

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

PR #9408: test(snapshot): add extended test cases for revert functionality

This PR is related as it addresses snapshot and revert functionality testing, which is directly relevant to the snapshot/revert issues being fixed in PR #9844.

However, this appears to be a test PR rather than a fix for the same issue, so it's more of a complementary PR than a true duplicate.

No duplicate PRs found addressing the same Windows non-ASCII filename snapshot issue.

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.