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/ScriptCodeFactoryStub.ts

@@ -1,5 +1,5 @@
-import type { ScriptCodeFactory } from '@/domain/ScriptCodeFactory';
-import type { IScriptCode } from '@/domain/IScriptCode';
+import type { ScriptCodeFactory } from '@/domain/Executables/Script/Code/ScriptCodeFactory';
+import type { ScriptCode } from '@/domain/Executables/Script/Code/ScriptCode';
 import { ScriptCodeStub } from './ScriptCodeStub';
 
 export function createScriptCodeFactoryStub(
@@ -17,6 +17,6 @@ export function createScriptCodeFactoryStub(
 }
 
 interface StubOptions {
-  readonly scriptCode?: IScriptCode;
+  readonly scriptCode?: ScriptCode;
   readonly defaultCodePrefix?: string;
 }