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.ts

@@ -0,0 +1,30 @@
+import { mediaContainer } from "./container.js";
+import { MEDIA_SYMBOLS } from "./symbols.js";
+import { MockMediaRepository } from "../infrastructure/repositories/media.repository.mock.js";
+import { buildDevMedia } from "../__seeds__/dev.js";
+import type { IMediaRepository } from "../application/repositories/media.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
+ * `bindProductionMedia(config)`. Tests must NOT call this — they construct
+ * `new MockMediaRepository()` 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 bindDevSeedMedia(): Promise<void> {
+  if (mediaContainer.isBound(MEDIA_SYMBOLS.IMediaRepository)) {
+    mediaContainer.unbind(MEDIA_SYMBOLS.IMediaRepository);
+  }
+
+  const repo = new MockMediaRepository();
+  for (const media of buildDevMedia()) {
+    await repo._store(media);
+  }
+
+  mediaContainer
+    .bind<IMediaRepository>(MEDIA_SYMBOLS.IMediaRepository)
+    .toConstantValue(repo);
+}