fix(tests): stabilize Windows test runs

[scarletkc]

Summary / 概要

• Stabilizes Windows test runs by removing platform-specific path, line-ending, executable-bit, and shell-resolution assumptions.

Why / 背景

• Windows test runs were failing because several tests and supporting paths assumed POSIX separators, LF-only Git behavior, executable mode bits, or WSL-compatible bash environment inheritance.

Changes / 变更

• Normalize Git repository and worktree paths before returning or comparing them.
• Use POSIX joins for Linux desktop/icon lookup paths.
• Force LF behavior in temporary Git checkpoint test repositories.
• Prefer Git Bash for workflow shell execution on Windows while preserving WORKFLOW_BASH_BIN.
• Normalize mac bundle candidate paths and avoid relying on executable bits for Contents/MacOS files on Windows.

Media / 截图或录屏

• Not applicable; no UI changes.

Tests / 测试

• Existing Windows-sensitive tests now pass; updated test setup for Git line-ending behavior.

Validation / 验证

• I agree that this contribution is submitted under the Contributor License Agreement. / 我同意本贡献遵循 Contributor License Agreement 提交。
• npm run test
• npm run typecheck
• npm run build
• npm run dev smoke: renderer dev server reached and Electron started.
• UI change: not applicable; no UI changes.
• Logic change: existing unit tests updated and passing.

Notes / 备注

• No linked issue.

[XingYu-Zhong]

Reviewed locally. Focused Windows-stabilization related tests passed in the local environment; no blocking issues found.