feat(features): add test factories to all 5 features

Adds src/__factories__/<entity>.factory.ts to auth, blog, marketing-pages,
navigation, media. Each factory uses defineFactory from @repo/core-testing
with stable date defaults (2026-01-01) so snapshot diffs reflect SUT
behavior only. Refactors mechanical inline-fixture tests to use factories.

Also adds vitest.config.ts and tsconfig path alias to @repo/media (lacked
both), and adds @repo/core-testing devDependency to @repo/media.

Spec: §5.1, §6.3

packages/blog/src/application/use-cases/get-articles.use-case.test.ts

@@ -3,6 +3,7 @@ import { blogContainer } from "../../di/container";
 import { BLOG_SYMBOLS } from "../../di/symbols";
 import type { IArticlesRepository } from "../../application/repositories/articles-repository.interface";
 import { MockArticlesRepository } from "../../infrastructure/repositories/mock-articles.repository";
+import { articleFactory } from "../../__factories__/article.factory";
 import { getArticlesUseCase } from "./get-articles.use-case";
 
 describe("getArticlesUseCase", () => {
@@ -16,47 +17,19 @@ describe("getArticlesUseCase", () => {
     blogContainer
       .bind<IArticlesRepository>(BLOG_SYMBOLS.IArticlesRepository)
       .toConstantValue(repo);
+    articleFactory.reset();
   });
 
   it("returns all articles with no filters", async () => {
-    const now = new Date();
-    await repo.createArticle({
-      id: "1",
-      title: "A",
-      slug: "a",
-      content: null,
-      status: "draft",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
+    await repo.createArticle(articleFactory.build({ id: "1", title: "A", slug: "a" }));
     const result = await getArticlesUseCase();
     expect(result).toHaveLength(1);
     expect(result[0]?.id).toBe("1");
   });
 
   it("filters by status", async () => {
-    const now = new Date();
-    await repo.createArticle({
-      id: "1",
-      title: "A",
-      slug: "a",
-      content: null,
-      status: "draft",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
-    await repo.createArticle({
-      id: "2",
-      title: "B",
-      slug: "b",
-      content: null,
-      status: "published",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
+    await repo.createArticle(articleFactory.build({ id: "1", title: "A", slug: "a", status: "draft" }));
+    await repo.createArticle(articleFactory.build({ id: "2", title: "B", slug: "b", status: "published" }));
     const result = await getArticlesUseCase({ status: "published" });
     expect(result).toHaveLength(1);
     expect(result[0]?.id).toBe("2");