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/navigation/src/di/bind-dev-seed.ts

@@ -0,0 +1,26 @@
+import { navigationContainer } from "./container.js";
+import { NAVIGATION_SYMBOLS } from "./symbols.js";
+import { MockHeaderRepository } from "../infrastructure/repositories/header.repository.mock.js";
+import { buildDevHeader } from "../__seeds__/dev.js";
+import type { IHeaderRepository } from "../application/repositories/header.repository.interface.js";
+
+/**
+ * Replace the default mock with a populated one for dev mode + storybook.
+ *
+ * Call this from app boot when `USE_DEV_SEED=true`, mutually exclusive with
+ * `bindProductionNavigation(config)`. Tests must NOT call this — they
+ * construct `new MockHeaderRepository()` 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 bindDevSeedNavigation(): Promise<void> {
+  if (navigationContainer.isBound(NAVIGATION_SYMBOLS.IHeaderRepository)) {
+    navigationContainer.unbind(NAVIGATION_SYMBOLS.IHeaderRepository);
+  }
+
+  navigationContainer
+    .bind<IHeaderRepository>(NAVIGATION_SYMBOLS.IHeaderRepository)
+    .toConstantValue(new MockHeaderRepository(buildDevHeader()));
+}