refactor: route bash app name validation through go

The bash and go validators previously each kept their own copy of the regex, which had to be updated in lockstep. Both bash wrappers now invoke the existing common binary via the same pattern as `verify_app_name`, leaving go as the single source of truth. The legacy `IsValidAppNameOld` rule is also widened to allow underscores again so apps created under the old naming rules can still be looked up through `VerifyAppName`'s either-rule fallback.

plugins/common/src/common/common.go

@@ -86,6 +86,12 @@ func main() {
 		} else {
 			fmt.Print("false")
 		}
+	case "is-valid-app-name":
+		appName := flag.Arg(1)
+		err = common.IsValidAppName(appName)
+	case "is-valid-app-name-old":
+		appName := flag.Arg(1)
+		err = common.IsValidAppNameOld(appName)
 	case "verify-app-name":
 		appName := flag.Arg(1)
 		err = common.VerifyAppName(appName)