[rush] Preserve unmanaged Git hooks and diagnose Git LFS conflicts

[Copilot]

Rush’s hook-directory cleanup can delete Git LFS hooks, allowing pointer commits to be pushed without their objects. Rush-generated LFS wrappers introduce the opposite failure: repeated git lfs install --local rejects them during Azure Pipelines checkout on reused workspaces.

• Ownership-aware installation

  • Replace only exact-match current or legacy Rush delegates; preserve unmanaged hooks, edited delegates, and symlinks.
  • Remove obsolete non-LFS delegates. Retain obsolete LFS delegates with a warning to avoid silently disabling uploads.

• Collision handling

  • Detect conflicting destination paths before changing any hooks, including case-insensitive matches and dangling symlinks.
  • Fail with actionable guidance; --bypass-policy skips installation rather than overwriting conflicts.

• LFS compatibility and recovery

  • Preserve canonical LFS hooks when their names are absent from common/git-hooks; placeholders are unnecessary.
  • Warn that custom Rush LFS wrappers remain incompatible with repeated LFS initialization.
  • Document recovery before the next checkout, without forcing replacement of legitimate custom hooks.

• Fixes [rush] Managed Git LFS hooks conflict with reused Azure Pipelines workspaces #6120