feat(blog): add bind-dev-seed binder + dev seed

Sets the canonical pattern for all 5 features. Three new files:

- src/__seeds__/dev.ts — buildDevArticles() function returning 3
  realistic articles (welcome, vertical-feature-architecture,
  wip-post) built from articleFactory with id/slug/title/status
  overrides only.
- src/di/bind-dev-seed.ts — bindDevSeedBlog() async function that
  unbinds IArticlesRepository, constructs MockArticlesRepository,
  seeds it via buildDevArticles(), and rebinds via .toConstantValue.
- src/di/bind-dev-seed.test.ts — 3 tests: populated repo, welcome
  article reachable by slug, idempotent (callable twice).

package.json adds the ./di/bind-dev-seed subpath export, parallel to
./di/bind-production.

Tests + use cases continue to construct MockArticlesRepository
directly — they never go through bindDevSeedBlog. The seed only attaches
when called explicitly at app boot.

packages/blog/src/di/bind-dev-seed.ts

@@ -0,0 +1,30 @@
+import { blogContainer } from "./container.js";
+import { BLOG_SYMBOLS } from "./symbols.js";
+import { MockArticlesRepository } from "../infrastructure/repositories/articles.repository.mock.js";
+import { buildDevArticles } from "../__seeds__/dev.js";
+import type { IArticlesRepository } from "../application/repositories/articles.repository.interface.js";
+
+/**
+ * Replace the default empty mock with a populated one for dev mode + storybook.
+ *
+ * Call this from app boot when `USE_DEV_SEED=true`, mutually exclusive with
+ * `bindProductionBlog(config)`. Tests must NOT call this — they construct
+ * `new MockArticlesRepository()` directly and seed via factories per-test.
+ *
+ * Idempotent: safe to call multiple times; each call rebuilds a fresh
+ * populated repo and rebinds the symbol.
+ */
+export async function bindDevSeedBlog(): Promise<void> {
+  if (blogContainer.isBound(BLOG_SYMBOLS.IArticlesRepository)) {
+    blogContainer.unbind(BLOG_SYMBOLS.IArticlesRepository);
+  }
+
+  const repo = new MockArticlesRepository();
+  for (const article of buildDevArticles()) {
+    await repo.createArticle(article);
+  }
+
+  blogContainer
+    .bind<IArticlesRepository>(BLOG_SYMBOLS.IArticlesRepository)
+    .toConstantValue(repo);
+}