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/SelectedScriptStub.ts

@@ -1,15 +1,15 @@
 import type { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
-import type { IScript } from '@/domain/IScript';
+import type { Script } from '@/domain/Executables/Script/Script';
 
 export class SelectedScriptStub implements SelectedScript {
-  public readonly script: IScript;
+  public readonly script: Script;
 
   public readonly id: string;
 
   public revert: boolean;
 
   constructor(
-    script: IScript,
+    script: Script,
   ) {
     this.id = script.id;
     this.script = script;