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/Category/CollectionCategory.ts

@@ -0,0 +1,59 @@
+import { BaseEntity } from '@/infrastructure/Entity/BaseEntity';
+import type { Category } from './Category';
+import type { Script } from '../Script/Script';
+
+export class CollectionCategory extends BaseEntity<number> implements Category {
+  private allSubScripts?: ReadonlyArray<Script> = undefined;
+
+  public readonly name: string;
+
+  public readonly docs: ReadonlyArray<string>;
+
+  public readonly subCategories: ReadonlyArray<Category>;
+
+  public readonly scripts: ReadonlyArray<Script>;
+
+  constructor(parameters: CategoryInitParameters) {
+    super(parameters.id);
+    validateParameters(parameters);
+    this.name = parameters.name;
+    this.docs = parameters.docs;
+    this.subCategories = parameters.subcategories;
+    this.scripts = parameters.scripts;
+  }
+
+  public includes(script: Script): boolean {
+    return this.getAllScriptsRecursively().some((childScript) => childScript.id === script.id);
+  }
+
+  public getAllScriptsRecursively(): readonly Script[] {
+    if (!this.allSubScripts) {
+      this.allSubScripts = parseScriptsRecursively(this);
+    }
+    return this.allSubScripts;
+  }
+}
+
+export interface CategoryInitParameters {
+  readonly id: number;
+  readonly name: string;
+  readonly docs: ReadonlyArray<string>;
+  readonly subcategories: ReadonlyArray<Category>;
+  readonly scripts: ReadonlyArray<Script>;
+}
+
+function parseScriptsRecursively(category: Category): ReadonlyArray<Script> {
+  return [
+    ...category.scripts,
+    ...category.subCategories.flatMap((c) => c.getAllScriptsRecursively()),
+  ];
+}
+
+function validateParameters(parameters: CategoryInitParameters) {
+  if (!parameters.name) {
+    throw new Error('missing name');
+  }
+  if (parameters.subcategories.length === 0 && parameters.scripts.length === 0) {
+    throw new Error('A category must have at least one sub-category or script');
+  }
+}