Add detection and hook support for jujutsu repositories:
- IsJujutsuRepo(): detects .jj directory
- IsColocatedJJGit(): detects colocated jj+git repos
- GetJujutsuRoot(): finds jj repo root
For colocated repos (jj git init --colocate):
- Install simplified hooks without staging (jj auto-commits working copy)
- Worktree handling preserved for git worktrees in colocated repos
For pure jj repos (no git):
- Print alias instructions since jj doesn't have native hooks yet
Closes: hq-ew1mbr.12
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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