Fix intent-to-add stash restore

[j178]

Closes #2142

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.49%. Comparing base (00b2520) to head (c2ca966).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2143      +/-   ##
==========================================
+ Coverage   92.39%   92.49%   +0.10%     
==========================================
  Files         122      122              
  Lines       25815    25813       -2     
==========================================
+ Hits        23853    23877      +24     
+ Misses       1962     1936      -26     

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[Copilot]

Pull request overview

This PR addresses #2142 by ensuring “intent-to-add” (git add -N/--intent-to-add) file contents are preserved when prek run stashes/restores unstaged changes and a conflicted patch restore forces a rollback of hook modifications.

Changes:

• Adds an integration test reproducing the conflicted stash-restore scenario with an intent-to-add file and validates file contents + intent-to-add status.
• Refactors WorkTreeKeeper to restore unstaged working tree contents before re-adding intent-to-add index entries (fixing the loss-of-content case).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
crates/prek/tests/run.rs	Adds a regression test for intent-to-add files surviving conflicted stash restore/rollback.
crates/prek/src/cli/run/keeper.rs	Refactors worktree cleanup/restore to enforce correct restore ordering and remove the global restore keeper.