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/__seeds__/dev.ts

@@ -0,0 +1,26 @@
+import { headerFactory } from "../__factories__/header.factory.js";
+import { navItemFactory } from "../__factories__/nav-item.factory.js";
+import type { Header } from "../entities/models/header.js";
+
+/**
+ * Realistic navigation seed for dev mode + storybook stories.
+ *
+ * Built from `headerFactory` and `navItemFactory` so factory defaults take
+ * care of boring fields and we only override what makes the nav look like a
+ * real site header.
+ *
+ * Lazily produced so importing this module is side-effect-free — the
+ * factory's sequence counter only advances when a binder calls
+ * `buildDevHeader()`.
+ */
+export function buildDevHeader(): Header {
+  return headerFactory.build({
+    logoId: "logo-main",
+    items: [
+      navItemFactory.build({ label: "Home", href: "/", external: false }),
+      navItemFactory.build({ label: "Blog", href: "/blog", external: false }),
+      navItemFactory.build({ label: "About", href: "/about", external: false }),
+      navItemFactory.build({ label: "Pricing", href: "/pricing", external: false }),
+    ],
+  });
+}