Add validation to command line flags + update system prompt handling

Renamed `applyPromptFlags` to `applyGenerationFlags` and added
`validateGenerationFlags`

pkg/util/util.go

@@ -21,7 +21,7 @@ func InputFromEditor(placeholder string, pattern string, content string) (string
 	msgFile, _ := os.CreateTemp("/tmp", pattern)
 	defer os.Remove(msgFile.Name())
 
-	os.WriteFile(msgFile.Name(), []byte(placeholder + content), os.ModeAppend)
+	os.WriteFile(msgFile.Name(), []byte(placeholder+content), os.ModeAppend)
 
 	editor := os.Getenv("EDITOR")
 	if editor == "" {
@@ -137,8 +137,8 @@ func SetStructDefaults(data interface{}) bool {
 		}
 
 		// Get the "default" struct tag
-		defaultTag := v.Type().Field(i).Tag.Get("default")
-		if defaultTag == "" {
+		defaultTag, ok := v.Type().Field(i).Tag.Lookup("default")
+		if (!ok) {
 			continue
 		}