fix: data race and overlay bugs (#20)

- redundant ghost text
- prompt deletion bug on overlay
- overlay bug on the non-exists commands

<img width="1152" height="221" alt="image"
src="https://github.com/user-attachments/assets/29ef0c1f-4cd8-4e36-960f-352010fc3bd1"
/>
<img width="1275" height="470" alt="image"
src="https://github.com/user-attachments/assets/aa765110-f9fa-49c8-94f2-767a827f5e5f"
/>
<img width="2517" height="152" alt="image"
src="https://github.com/user-attachments/assets/47a6668f-fb01-46be-9ad2-2c50c283f175"
/>

commands/core/lookup.go

@@ -272,6 +272,7 @@ func Lookup(input string) []Suggestion {
 }
 
 func topLevelSuggestions(query string, aliases map[string]string) []Suggestion {
+	scanExternalCommands()
 	results, seen := []Suggestion{}, make(map[string]bool)
 
 	for name, target := range aliases {