fix: replace Directus SDK with native fetch for featured content

Replace customEndpoint() with native fetch in getFeaturedModels() and
getFeaturedVideos() to return plain JSON instead of non-serializable
Directus SDK objects. This resolves the SvelteKit serialization error:
"Cannot stringify arbitrary non-POJOs".

Changes:
- Use native fetch with PUBLIC_URL instead of getDirectusInstance()
- Return plain JSON via response.json() instead of SDK request objects
- Remove JSON.parse(JSON.stringify()) serialization hack from +page.server.ts
- Rename fetch parameter to fetchFn for clarity

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/frontend/src/routes/+page.server.ts

@@ -1,13 +1,7 @@
 import { getFeaturedModels, getFeaturedVideos } from "$lib/services";
 export async function load({ fetch }) {
-	const [models, videos] = await Promise.all([
-		getFeaturedModels(3, fetch),
-		getFeaturedVideos(3, fetch),
-	]);
-
-	// Ensure data is serializable by converting to plain JSON
 	return {
-		models: JSON.parse(JSON.stringify(models)),
-		videos: JSON.parse(JSON.stringify(videos)),
+		models: await getFeaturedModels(3, fetch),
+		videos: await getFeaturedVideos(3, fetch),
 	};
 }