fix: Resolve 11 errcheck linter violations to unblock CI (bd-91)

Fixed all unchecked error returns in production code:
- os.Remove() calls in cleanup paths
- cmd.Wait() in goroutines
- fmt.Fprintf() writes
- Type assertions with proper ok checks

Reduces linter issues from 99 to 88. CI should now pass linting.

cmd/bd/repos.go

@@ -18,7 +18,7 @@ var reposCmd = &cobra.Command{
 This command requires a running global daemon (bd daemon --global).
 It allows you to view and aggregate work across all cached repositories.`,
 	Run: func(cmd *cobra.Command, args []string) {
-		cmd.Help()
+		_ = cmd.Help()
 	},
 }