refactor: use explicit env vars in docker-compose files

Replace env_file with explicit environment variables to allow
composing grist-mcp with other services without .env conflicts.

deploy/dev/docker-compose.yml

@@ -9,8 +9,9 @@ services:
     volumes:
       - ../../src:/app/src:ro
       - ../../config.yaml:/app/config.yaml:ro
-    env_file:
-      - .env
+    environment:
+      - GRIST_MCP_TOKEN=${GRIST_MCP_TOKEN}
+      - CONFIG_PATH=/app/config.yaml
     healthcheck:
       test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:3000/health')"]
       interval: 30s

deploy/prod/docker-compose.yml

@@ -8,8 +8,9 @@ services:
       - "${PORT:-3000}:3000"
     volumes:
       - ./config.yaml:/app/config.yaml:ro
-    env_file:
-      - .env
+    environment:
+      - GRIST_MCP_TOKEN=${GRIST_MCP_TOKEN}
+      - CONFIG_PATH=/app/config.yaml
     restart: unless-stopped
     deploy:
       resources: