fix(lint): resolve all golangci-lint errors

- Mark unused ctx parameter with underscore in getRepoRootForWorktree
- Replace exec.Command("test", "-d") with os.Stat for directory check
- Handle file.Close() errors properly in compact.go and migrate_tombstones.go
- Explicitly ignore cleanup errors with _ assignment

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

cmd/bd/compact.go

@@ -1019,7 +1019,9 @@ func pruneExpiredTombstones() (*TombstonePruneResult, error) {
 		}
 		allIssues = append(allIssues, &issue)
 	}
-	file.Close()
+	if err := file.Close(); err != nil {
+		return nil, fmt.Errorf("failed to close issues file: %w", err)
+	}
 
 	// Determine TTL
 	ttl := types.DefaultTombstoneTTL
@@ -1052,20 +1054,20 @@ func pruneExpiredTombstones() (*TombstonePruneResult, error) {
 	encoder := json.NewEncoder(tempFile)
 	for _, issue := range kept {
 		if err := encoder.Encode(issue); err != nil {
-			tempFile.Close()
-			os.Remove(tempPath)
+			_ = tempFile.Close()
+			_ = os.Remove(tempPath)
 			return nil, fmt.Errorf("failed to write issue %s: %w", issue.ID, err)
 		}
 	}
 
 	if err := tempFile.Close(); err != nil {
-		os.Remove(tempPath)
+		_ = os.Remove(tempPath)
 		return nil, fmt.Errorf("failed to close temp file: %w", err)
 	}
 
 	// Atomically replace
 	if err := os.Rename(tempPath, issuesPath); err != nil {
-		os.Remove(tempPath)
+		_ = os.Remove(tempPath)
 		return nil, fmt.Errorf("failed to replace issues.jsonl: %w", err)
 	}
 

cmd/bd/migrate_tombstones.go

@@ -128,7 +128,7 @@ Examples:
 					existingTombstones[issue.ID] = true
 				}
 			}
-			file.Close()
+			_ = file.Close()
 		}
 
 		// Determine which deletions need migration

cmd/bd/sync.go

@@ -836,7 +836,7 @@ func gitHasChanges(ctx context.Context, filePath string) (bool, error) {
 
 // getRepoRootForWorktree returns the main repository root for running git commands
 // This is always the main repository root, never the worktree root
-func getRepoRootForWorktree(ctx context.Context) string {
+func getRepoRootForWorktree(_ context.Context) string {
 	repoRoot, err := git.GetMainRepoRoot()
 	if err != nil {
 		// Fallback to current directory if GetMainRepoRoot fails

internal/git/gitdir.go

@@ -2,6 +2,7 @@ package git
 
 import (
 	"fmt"
+	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
@@ -106,7 +107,7 @@ func GetMainRepoRoot() (string, error) {
 		commonDir := getGitDirNoError("--git-common-dir")
 		if commonDir != "" {
 			// Validate that commonDir exists
-			if _, err := exec.Command("test", "-d", commonDir).Output(); err == nil {
+			if info, err := os.Stat(commonDir); err == nil && info.IsDir() {
 				return filepath.Dir(commonDir), nil
 			}
 		}