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/CategoryDataStub.ts

@@ -1,14 +1,14 @@
-import type { CategoryData, CategoryOrScriptData, DocumentationData } from '@/application/collections/';
+import type { CategoryData, ExecutableData, DocumentationData } from '@/application/collections/';
 import { createScriptDataWithCode } from '@tests/unit/shared/Stubs/ScriptDataStub';
 
 export class CategoryDataStub implements CategoryData {
-  public children: readonly CategoryOrScriptData[] = [createScriptDataWithCode()];
+  public children: readonly ExecutableData[] = [createScriptDataWithCode()];
 
   public category = 'category name';
 
   public docs?: DocumentationData;
 
-  public withChildren(children: readonly CategoryOrScriptData[]) {
+  public withChildren(children: readonly ExecutableData[]) {
     this.children = children;
     return this;
   }