Fix docker-compose.yml syntax

Add the missing colons after `networks` (service) and `chromanet`
(top-level) so Compose can parse the file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -13,9 +13,9 @@ services:
     env_file:
       - path: .env
         required: false
-    networks
+    networks:
       - chromanet
 
 networks:
-  chromanet
+  chromanet:
     external: true