Enable parallel checkout for faster worktree creation

Add EnableParallelCheckout() helper to git package and call it when
creating bare repos. This configures checkout.workers=0 (auto-detect
cores) and checkout.thresholdForParallelism=100.

Expected 2-8x speedup on SSD for large repos (e.g., java rig with 85k files).
Based on research in hq-dqc7t (APFS CoW optimization).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/git/git.go

@@ -442,10 +442,10 @@ func (g *Git) CommitAll(message string) error {
 
 // GitStatus represents the status of the working directory.
 type GitStatus struct {
-	Clean    bool
-	Modified []string
-	Added    []string
-	Deleted  []string
+	Clean     bool
+	Modified  []string
+	Added     []string
+	Deleted   []string
 	Untracked []string
 }
 
@@ -767,6 +767,22 @@ func (g *Git) IsAncestor(ancestor, descendant string) (bool, error) {
 	return true, nil
 }
 
+// EnableParallelCheckout configures git to use parallel workers during checkout.
+// This can significantly speed up worktree creation on SSDs (2-8x for large repos).
+// Setting workers=0 auto-detects the number of CPU cores.
+// Safe to call multiple times - git config is idempotent.
+func (g *Git) EnableParallelCheckout() error {
+	// Auto-detect number of workers (0 = number of logical cores)
+	if _, err := g.run("config", "checkout.workers", "0"); err != nil {
+		return fmt.Errorf("setting checkout.workers: %w", err)
+	}
+	// Only parallelize when there are enough files to benefit
+	if _, err := g.run("config", "checkout.thresholdForParallelism", "100"); err != nil {
+		return fmt.Errorf("setting checkout.thresholdForParallelism: %w", err)
+	}
+	return nil
+}
+
 // WorktreeAdd creates a new worktree at the given path with a new branch.
 // The new branch is created from the current HEAD.
 // Sparse checkout is enabled to exclude .claude/ from source repos.
@@ -1135,8 +1151,8 @@ type UncommittedWorkStatus struct {
 	StashCount            int
 	UnpushedCommits       int
 	// Details for error messages
-	ModifiedFiles   []string
-	UntrackedFiles  []string
+	ModifiedFiles  []string
+	UntrackedFiles []string
 }
 
 // Clean returns true if there is no uncommitted work.