Use shared Docker network to connect to btcdata independently

Remove btcdata compose include, use external shared network instead
so both projects can run as separate Docker stacks.

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

docker-compose.yml

@@ -1,9 +1,15 @@
-include:
+networks:
-  - path: ../btcdata/docker-compose.yml
+  shared:
+    name: shared
+    external: true
 
 services:
   btcprice:
     build: .
     restart: unless-stopped
+    networks:
+      - shared
     ports:
       - "4041:4040"
+    environment:
+      BTCDATA_URL: "http://btcdata:${DOCKER_BTCDATA_PORT:-4102}"