Fix dev compose: preserve node_modules via named volumes

Mounting ./server:/app/server overwrote the npm-installed node_modules
from the Docker build. Named volumes for server/client node_modules
shadow the bind mount so installed packages are preserved.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -2,8 +2,14 @@ services:
   app:
     volumes:
       - ./server:/app/server
+      - server_node_modules:/app/server/node_modules
       - ./client:/app/client
+      - client_node_modules:/app/client/node_modules
     ports:
       - "5173:5173"
     environment:
       NODE_ENV: development
+
+volumes:
+  server_node_modules:
+  client_node_modules: