refactor(blog): factory-style use cases + per-use-case controllers + getArticleBySlug

- Use cases (create-article, get-articles, get-article-by-slug NEW) → factory functions
- Controllers split: articles.controller.ts → 3 single-responsibility files
- DI module wires factories with .toDynamicValue()
- tRPC router resolves controllers via container

Refactor log: §2, §3, §4.1, §4.2, §5.1
Spec: §6.2

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/blog/src/interface-adapters/controllers/get-article-by-slug.controller.ts

@@ -0,0 +1,21 @@
+import { z } from "zod";
+
+import { InputParseError } from "../../entities/errors/common";
+import type { Article } from "../../entities/models/article";
+import type { IGetArticleBySlugUseCase } from "../../application/use-cases/get-article-by-slug.use-case";
+
+const inputSchema = z.object({
+  slug: z.string().min(1),
+});
+
+export type IGetArticleBySlugController = ReturnType<typeof getArticleBySlugController>;
+
+export const getArticleBySlugController =
+  (getArticleBySlugUseCase: IGetArticleBySlugUseCase) =>
+  async (input: Partial<z.infer<typeof inputSchema>>): Promise<Article> => {
+    const parsed = inputSchema.safeParse(input);
+    if (!parsed.success) {
+      throw new InputParseError("Invalid get-article-by-slug input", { cause: parsed.error });
+    }
+    return getArticleBySlugUseCase(parsed.data);
+  };