fix: resolve lint errors blocking CI

- Add explicit error checking for fmt.Fprintf/Fprintln in claude.go
- Add gosec nolint for safe exec.CommandContext calls in sync_git.go
- Remove unused error return from findTownRoutes in routes.go

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

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

cmd/bd/sync_git.go

@@ -387,7 +387,7 @@ func gitPull(ctx context.Context) error {
 	remote := strings.TrimSpace(string(remoteOutput))
 
 	// Pull with explicit remote and branch
-	cmd := exec.CommandContext(ctx, "git", "pull", remote, branch)
+	cmd := exec.CommandContext(ctx, "git", "pull", remote, branch) //nolint:gosec // G204: remote/branch from git config, not user input
 	output, err := cmd.CombinedOutput()
 	if err != nil {
 		return fmt.Errorf("git pull failed: %w\n%s", err, output)
@@ -422,7 +422,7 @@ func restoreBeadsDirFromBranch(ctx context.Context) error {
 
 	// Restore .beads/ from HEAD (current branch's committed state)
 	// Using -- to ensure .beads/ is treated as a path, not a branch name
-	cmd := exec.CommandContext(ctx, "git", "checkout", "HEAD", "--", beadsDir)
+	cmd := exec.CommandContext(ctx, "git", "checkout", "HEAD", "--", beadsDir) //nolint:gosec // G204: beadsDir from FindBeadsDir(), not user input
 	output, err := cmd.CombinedOutput()
 	if err != nil {
 		return fmt.Errorf("git checkout failed: %w\n%s", err, output)