fix: Preserve symlinked manifest paths

[claydugo]

Description

This PR fixes an issue where pixi resolves symlinked pixi.toml files to their real location, causing the .pixi/ directory to be created relative to the symlink target instead of the symlink itself. This broke common dotfiles management workflows where users symlink config files from a git repository to their home directory.

Fixes #4907

How Has This Been Tested?

Test was added to crates/pixi_manifest/src/manifests/provenance.rs and I tested the described workflow locally with the generated binary.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude Code with body of issue I wrote

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added sufficient tests to cover my changes.

[baszalmstra]

Thanks!