fix: preserve unrelated unstaged changes on conflict

[Sakshamm-Goyal]

Closes #1480

Context

When the hidden patch for a partially staged file conflicts with hook output, Lefthook resets the whole tracked worktree before replaying only the partial-file patch. That restores the conflicting file, but silently discards pre-existing unstaged changes in unrelated tracked files.

Changes

• Save a full pre-hook unstaged patch alongside the partial-file patch.
• Keep the existing partial patch on the normal successful restore path.
• After conflict recovery resets hook output, replay the full patch so every pre-existing unstaged change is restored.
• Remove both temporary patches and the auto-backup stash after a successful restore.
• Add a real-Git regression covering a partially staged conflict plus an unrelated unstaged tracked file.

Validation

• make test
• affected restore integration scenarios with the race detector
• all integration scripts except the timing-sensitive run_interrupt script in one race-enabled batch
• run_interrupt separately with the race detector
• make lint (0 issues)

AI usage

Prepared with Codex; the behavior is covered by the fail-first integration regression and repository test commands listed above.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

_{Reviews (2): Last reviewed commit: "fix: preserve recovery error context" | Re-trigger Greptile}

Context used:

• Context used - AGENTS.md (source)