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/auth/src/__factories__/index.ts

@@ -0,0 +1,2 @@
+export { userFactory } from "./user.factory.js";
+export { sessionFactory } from "./session.factory.js";

packages/auth/src/__factories__/session.factory.test.ts

@@ -0,0 +1,26 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { sessionFactory } from "@/__factories__/session.factory";
+
+describe("sessionFactory", () => {
+  beforeEach(() => sessionFactory.reset());
+
+  it("returns a Session with stable defaults", () => {
+    const s = sessionFactory.build();
+    expect(s.id).toBe("session-1");
+    expect(s.userId).toBe("user-1");
+    expect(s.expiresAt).toBeInstanceOf(Date);
+  });
+
+  it("applies overrides", () => {
+    const s = sessionFactory.build({ userId: "user-42" });
+    expect(s.userId).toBe("user-42");
+    expect(s.id).toBe("session-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = sessionFactory.build();
+    const b = sessionFactory.build();
+    expect(a.id).toBe("session-1");
+    expect(b.id).toBe("session-2");
+  });
+});

packages/auth/src/__factories__/session.factory.ts

@@ -0,0 +1,8 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { Session } from "../entities/session.js";
+
+export const sessionFactory = defineFactory<Session>(({ sequence }) => ({
+  id: `session-${sequence}`,
+  userId: "user-1",
+  expiresAt: new Date("2026-12-31T23:59:59Z"),
+}));

packages/auth/src/__factories__/user.factory.test.ts

@@ -0,0 +1,26 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { userFactory } from "@/__factories__/user.factory";
+
+describe("userFactory", () => {
+  beforeEach(() => userFactory.reset());
+
+  it("returns a User with stable defaults", () => {
+    const u = userFactory.build();
+    expect(u.id).toBe("user-1");
+    expect(u.username).toBe("user1");
+    expect(u.passwordHash).toHaveLength(60);
+  });
+
+  it("applies overrides", () => {
+    const u = userFactory.build({ username: "alice" });
+    expect(u.username).toBe("alice");
+    expect(u.id).toBe("user-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = userFactory.build();
+    const b = userFactory.build();
+    expect(a.id).toBe("user-1");
+    expect(b.id).toBe("user-2");
+  });
+});

packages/auth/src/__factories__/user.factory.ts

@@ -0,0 +1,8 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { User } from "../entities/user.js";
+
+export const userFactory = defineFactory<User>(({ sequence }) => ({
+  id: `user-${sequence}`,
+  username: `user${sequence}`,
+  passwordHash: `$2b$10$stablehashfortest${sequence}`.padEnd(60, "x"),
+}));