Fix Amplify environment variable configuration

- Add amplify.yml for proper build configuration
- Update next.config.ts to expose YOUTUBE_API_KEY env var
- This should fix the issue with secrets not being available in production

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

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

amplify/backend.ts

@@ -1,11 +1,11 @@
-import { defineBackend } from '@aws-amplify/backend';
-import { auth } from './auth/resource';
-import { data } from './data/resource';
-
-/**
- * @see https://docs.amplify.aws/react/build-a-backend/ to add storage, functions, and more
- */
-defineBackend({
-  auth,
-  data,
-});
+import { defineBackend } from '@aws-amplify/backend';
+import { auth } from './auth/resource';
+import { data } from './data/resource';
+
+/**
+ * @see https://docs.amplify.aws/react/build-a-backend/ to add storage, functions, and more
+ */
+defineBackend({
+  auth,
+  data,
+});