fix(desktop): retry shell env probe after timeout

[lazyayuan]

Issue for this PR

Follow-up to #26449.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When the interactive login-shell environment probe exceeds its five-second timeout, Desktop currently falls back directly to the minimal app environment. That can drop Homebrew and user-local paths even though the cheaper login-only probe would succeed.

Retry with -l after an -il timeout, matching the existing fallback for other probe failures. This keeps slow interactive startup files from causing intermittent command not found errors.

How did you verify your code works?

• npx --yes bun@1.3.14 test src/main/shell-env.test.ts from packages/desktop (6 passed)
• Reproduced the GUI launch environment with PATH=/usr/bin:/bin:/usr/sbin:/sbin; zsh -lc resolved both uv and ffmpeg
• Measured zsh -lc at about 0.1 seconds versus 1.2-1.8 seconds for zsh -ilc locally
• Package typecheck could not run in this checkout because tsgo is not installed

Screenshots / recordings

N/A - no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

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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

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