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/__seeds__/dev.ts

@@ -0,0 +1,35 @@
+import { articleFactory } from "../__factories__/article.factory.js";
+import type { Article } from "../entities/models/article.js";
+
+/**
+ * Realistic blog seed for dev mode + storybook stories.
+ *
+ * Built from `articleFactory` so factory defaults take care of the boring
+ * fields (createdAt, updatedAt, content, authorId) and we only override what
+ * makes the data look like a populated database.
+ *
+ * Lazily produced so importing this module is side-effect-free — the factory's
+ * sequence counter only advances when a binder calls `buildDevArticles()`.
+ */
+export function buildDevArticles(): Article[] {
+  return [
+    articleFactory.build({
+      id: "welcome",
+      slug: "welcome",
+      title: "Welcome to the blog",
+      status: "published",
+    }),
+    articleFactory.build({
+      id: "vertical-feature-architecture",
+      slug: "vertical-feature-architecture",
+      title: "Why vertical-feature packages",
+      status: "published",
+    }),
+    articleFactory.build({
+      id: "wip-post",
+      slug: "work-in-progress",
+      title: "A draft we haven't shipped yet",
+      status: "draft",
+    }),
+  ];
+}