fix(env): unset session override when vp env use called without arguments

[JasonOA888]

Fixes #951

When vp env use is called without a version argument, it should revert to file-based Node.js version resolution instead of keeping the session override from VITE_PLUS_NODE_VERSION env var or session file.

Changes:

• Add resolve_version_from_files() to resolve version skipping session overrides
• Update vp env use to unset session override before resolving when no arg provided
• This allows users to temporarily override with vp env use 22 and revert with vp env use

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[fengmk2]

Can you refer to the current unit tests or snap tests in the project and add test cases corresponding to this change?

[JasonOA888]

Good call! I've added unit tests following the existing test patterns in config.rs:

• test_resolve_version_from_files_ignores_env_var - verifies env var override is skipped
• test_resolve_version_from_files_ignores_session_file - verifies session file override is skipped
• test_resolve_version_still_respects_overrides - verifies existing resolve_version behavior is unchanged

Commit: 1c84e2e

[fengmk2]

Please fix CI fails.

[JasonOA888]

Hi @fengmk2, I see the CI is failing. I checked the logs and it looks like there are issues in cargo check and cargo shear. However, the code compiles fine locally.

Could you help me understand the specific errors? The GitHub Actions UI shows failures but I cannot access the detailed logs directly.

[fengmk2]

@JasonOA888 I will take over to fix the remaining issues and merge after manual testing. Thank you for the contribution!

[fengmk2]

signed commits required is disable, will merge after ci pass.