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/CollectionDataStub.ts

@@ -1,7 +1,7 @@
 import type {
   CategoryData, ScriptData, CollectionData, ScriptingDefinitionData, FunctionData,
 } from '@/application/collections/';
-import { RecommendationLevel } from '@/domain/RecommendationLevel';
+import { RecommendationLevel } from '@/domain/Executables/Script/RecommendationLevel';
 import { ScriptingLanguage } from '@/domain/ScriptingLanguage';
 import { createScriptDataWithCode } from './ScriptDataStub';