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.

src/domain/Executables/Script/Script.ts

@@ -0,0 +1,11 @@
+import { RecommendationLevel } from './RecommendationLevel';
+import type { Executable } from '../Executable';
+import type { Documentable } from '../Documentable';
+import type { ScriptCode } from './Code/ScriptCode';
+
+export interface Script extends Executable<string>, Documentable {
+  readonly name: string;
+  readonly level?: RecommendationLevel;
+  readonly code: ScriptCode;
+  canRevert(): boolean;
+}