feat(blog): add Article entity with rich-text content + domain errors

packages/blog/src/entities/errors.ts

@@ -0,0 +1,11 @@
+export class ArticleNotFoundError extends Error {
+  constructor(message = "Article not found", options?: ErrorOptions) {
+    super(message, options);
+  }
+}
+
+export class InputParseError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+  }
+}