Refactor to unify scripts/categories as Executable

This commit consolidates scripts and categories under a unified
'Executable' concept. This simplifies the architecture and improves code
readability.

- Introduce subfolders within `src/domain` to segregate domain elements.
- Update class and interface names by removing the 'I' prefix in
  alignment with new coding standards.
- Replace 'Node' with 'Executable' to clarify usage; reserve 'Node'
  exclusively for the UI's tree component.

tests/unit/shared/Stubs/SyntaxFactoryStub.ts

@@ -0,0 +1,18 @@
+import type { ILanguageSyntax } from '@/application/Parser/Executable/Script/Validation/Syntax/ILanguageSyntax';
+import type { ISyntaxFactory } from '@/application/Parser/Executable/Script/Validation/Syntax/ISyntaxFactory';
+import type { ScriptingLanguage } from '@/domain/ScriptingLanguage';
+import { LanguageSyntaxStub } from './LanguageSyntaxStub';
+
+export function createSyntaxFactoryStub(
+  expectedLanguage?: ScriptingLanguage,
+  result?: ILanguageSyntax,
+): ISyntaxFactory {
+  return {
+    create: (language: ScriptingLanguage) => {
+      if (expectedLanguage !== undefined && language !== expectedLanguage) {
+        throw new Error('unexpected language');
+      }
+      return result ?? new LanguageSyntaxStub();
+    },
+  };
+}