feat: add Git worktree compatibility (PR #478)

Adds comprehensive Git worktree support for beads issue tracking:

Core changes:
- New internal/git/gitdir.go package for worktree detection
- GetGitDir() returns proper .git location (main repo, not worktree)
- Updated all hooks to use git.GetGitDir() instead of local helper
- BeadsDir() now prioritizes main repository's .beads directory

Features:
- Hooks auto-install in main repo when run from worktree
- Shared .beads directory across all worktrees
- Config option no-install-hooks to disable auto-install
- New bd worktree subcommand for diagnostics

Documentation:
- New docs/WORKTREES.md with setup instructions
- Updated CHANGELOG.md and AGENT_INSTRUCTIONS.md

Testing:
- Updated tests to use exported git.GetGitDir()
- Added worktree detection tests

Co-authored-by: Claude <noreply@anthropic.com>
Closes: #478

internal/storage/sqlite/sqlite_bench_test.go

@@ -139,103 +139,6 @@ func BenchmarkGetReadyWork_FromJSONL(b *testing.B) {
 	})
 }
 
-// BenchmarkLargeDescription benchmarks handling of issues with very large descriptions (100KB+)
-func BenchmarkLargeDescription(b *testing.B) {
-	runBenchmark(b, setupLargeBenchDB, func(store *SQLiteStorage, ctx context.Context) error {
-		// Create issue with 100KB description
-		largeDesc := make([]byte, 100*1024)
-		for i := range largeDesc {
-			largeDesc[i] = byte('a' + (i % 26))
-		}
-
-		issue := &types.Issue{
-			Title:       "Issue with large description",
-			Description: string(largeDesc),
-			Status:      types.StatusOpen,
-			Priority:    2,
-			IssueType:   types.TypeTask,
-		}
-		return store.CreateIssue(ctx, issue, "bench")
-	})
-}
-
-// BenchmarkBulkCloseIssues benchmarks closing 100 issues in sequence
-func BenchmarkBulkCloseIssues(b *testing.B) {
-	store, cleanup := setupLargeBenchDB(b)
-	defer cleanup()
-	ctx := context.Background()
-
-	// Get 100 open issues to close
-	openStatus := types.StatusOpen
-	issues, err := store.SearchIssues(ctx, "", types.IssueFilter{
-		Status: &openStatus,
-		Limit:  100,
-	})
-	if err != nil || len(issues) < 100 {
-		b.Fatalf("Failed to get 100 issues for bulk close test: got %d, err %v", len(issues), err)
-	}
-
-	b.ResetTimer()
-	b.ReportAllocs()
-
-	for i := 0; i < b.N; i++ {
-		for j, issue := range issues {
-			if err := store.CloseIssue(ctx, issue.ID, "Bulk closed", "bench"); err != nil {
-				b.Fatalf("CloseIssue failed: %v", err)
-			}
-			// Re-open for next iteration (except last one)
-			if j < len(issues)-1 {
-				updates := map[string]interface{}{"status": types.StatusOpen}
-				if err := store.UpdateIssue(ctx, issue.ID, updates, "bench"); err != nil {
-					b.Fatalf("UpdateIssue failed: %v", err)
-				}
-			}
-		}
-	}
-}
-
-// BenchmarkSyncMerge benchmarks JSONL merge operations (simulating full sync cycle)
-func BenchmarkSyncMerge(b *testing.B) {
-	store, cleanup := setupLargeBenchDB(b)
-	defer cleanup()
-	ctx := context.Background()
-
-	// For each iteration, simulate a sync by creating and updating issues
-	b.ResetTimer()
-	b.ReportAllocs()
-
-	for i := 0; i < b.N; i++ {
-		// Simulate incoming changes: create 10 new issues, update 10 existing
-		for j := 0; j < 10; j++ {
-			issue := &types.Issue{
-				Title:       "Synced issue",
-				Description: "Incoming change",
-				Status:      types.StatusOpen,
-				Priority:    2,
-				IssueType:   types.TypeTask,
-			}
-			if err := store.CreateIssue(ctx, issue, "sync"); err != nil {
-				b.Fatalf("CreateIssue failed: %v", err)
-			}
-		}
-
-		// Update 10 existing issues
-		openStatus := types.StatusOpen
-		issues, err := store.SearchIssues(ctx, "", types.IssueFilter{
-			Status: &openStatus,
-			Limit:  10,
-		})
-		if err == nil && len(issues) > 0 {
-			for _, issue := range issues {
-				updates := map[string]interface{}{
-					"title": "Updated from sync",
-				}
-				_ = store.UpdateIssue(ctx, issue.ID, updates, "sync")
-			}
-		}
-	}
-}
-
 // Helper function
 func intPtr(i int) *int {
 	return &i