feat(features): add bind-dev-seed binders for auth/marketing-pages/navigation/media

Mirrors the canonical blog pattern landed earlier on this branch.

Per feature:
- src/__seeds__/dev.ts — lazy buildDev<Entities>() function using the
  feature's existing factory for sensible defaults
- src/di/bind-dev-seed.ts — bindDevSeed<Feature>() async function that
  rebinds the repo symbol(s) to a populated MockXRepository via
  .toConstantValue
- src/di/bind-dev-seed.test.ts — 3+ tests per feature (populates,
  reachable by id/slug, idempotent)
- package.json — adds ./di/bind-dev-seed subpath export

Tests + use cases continue to construct mocks directly; the seed never
runs from a *.test.ts path. App boot wiring (USE_DEV_SEED env branch)
follows in a separate commit.

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

packages/media/src/di/bind-dev-seed.test.ts

@@ -0,0 +1,71 @@
+import "reflect-metadata";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { bindDevSeedMedia } from "@/di/bind-dev-seed";
+import { mediaContainer } from "@/di/container";
+import { MEDIA_SYMBOLS } from "@/di/symbols";
+import { MockMediaRepository } from "@/infrastructure/repositories/media.repository.mock";
+import type { IMediaRepository } from "@/application/repositories/media.repository.interface";
+
+describe("bindDevSeedMedia", () => {
+  // Each test starts from the default empty-mock binding and tears down
+  // afterwards so the global mediaContainer state stays clean for siblings.
+  beforeEach(() => {
+    if (mediaContainer.isBound(MEDIA_SYMBOLS.IMediaRepository)) {
+      mediaContainer.unbind(MEDIA_SYMBOLS.IMediaRepository);
+    }
+    mediaContainer
+      .bind<IMediaRepository>(MEDIA_SYMBOLS.IMediaRepository)
+      .to(MockMediaRepository);
+  });
+
+  afterEach(() => {
+    if (mediaContainer.isBound(MEDIA_SYMBOLS.IMediaRepository)) {
+      mediaContainer.unbind(MEDIA_SYMBOLS.IMediaRepository);
+    }
+    mediaContainer
+      .bind<IMediaRepository>(MEDIA_SYMBOLS.IMediaRepository)
+      .to(MockMediaRepository);
+  });
+
+  it("populates the repository with the dev media entries", async () => {
+    await bindDevSeedMedia();
+
+    const repo = mediaContainer.get<IMediaRepository>(
+      MEDIA_SYMBOLS.IMediaRepository,
+    );
+    const all = await repo.listMedia();
+
+    expect(all.length).toBeGreaterThan(0);
+  });
+
+  it("seeds placeholder-1 reachable by id", async () => {
+    await bindDevSeedMedia();
+
+    const repo = mediaContainer.get<IMediaRepository>(
+      MEDIA_SYMBOLS.IMediaRepository,
+    );
+    const item = await repo.getMedia("placeholder-1");
+
+    expect(item).toBeDefined();
+    expect(item?.url).toBe("/dev/placeholder-1.jpg");
+    expect(item?.alt).toBe("Hero background image");
+  });
+
+  it("is idempotent — calling twice rebuilds a fresh populated repo", async () => {
+    await bindDevSeedMedia();
+    const before = mediaContainer.get<IMediaRepository>(
+      MEDIA_SYMBOLS.IMediaRepository,
+    );
+    const beforeCount = (await before.listMedia()).length;
+
+    await bindDevSeedMedia();
+    const after = mediaContainer.get<IMediaRepository>(
+      MEDIA_SYMBOLS.IMediaRepository,
+    );
+    const afterCount = (await after.listMedia()).length;
+
+    expect(afterCount).toBe(beforeCount);
+    // It's a fresh instance — not the previous one.
+    expect(after).not.toBe(before);
+  });
+});