fix: schemas Sanity en plain objects + config images CDN

- Retire embedded Sanity Studio (incompatible React 18)
- Schemas en plain JS pour documentation/copie vers Studio séparé
- Ajoute config images Sanity CDN dans next.config.ts

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

next.config.ts

@@ -1,5 +1,15 @@
 import type { NextConfig } from "next";
 
-const nextConfig: NextConfig = {};
+const nextConfig: NextConfig = {
+  // Allow Sanity image CDN
+  images: {
+    remotePatterns: [
+      {
+        protocol: "https",
+        hostname: "cdn.sanity.io",
+      },
+    ],
+  },
+};
 
 export default nextConfig;