feat: add routes index file with auth routes registration

backend/src/routes/index.ts

@@ -0,0 +1,19 @@
+import { FastifyInstance } from 'fastify';
+import authRoutes from './auth';
+
+export default async function routes(fastify: FastifyInstance) {
+  // Register all route groups
+  fastify.register(authRoutes, { prefix: '/auth' });
+  
+  // TODO: Register other route groups when implemented
+  // fastify.register(projectsRoutes, { prefix: '/projects' });
+  // fastify.register(layersRoutes, { prefix: '/layers' });
+  // fastify.register(elementsRoutes, { prefix: '/elements' });
+  // fastify.register(blocksRoutes, { prefix: '/blocks' });
+  // fastify.register(importRoutes, { prefix: '/import' });
+  // fastify.register(exportRoutes, { prefix: '/export' });
+  // fastify.register(pluginsRoutes, { prefix: '/plugins' });
+  // fastify.register(aiRoutes, { prefix: '/ai' });
+  // fastify.register(usersRoutes, { prefix: '/users' });
+  // fastify.register(settingsRoutes, { prefix: '/settings' });
+}