Rename shared network to btc-network, remove default network

- All services use btc-network exclusively
- Increase Frankfurter retry to 12x10s for cold start resilience

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

docker-compose.yml

@@ -1,6 +1,6 @@
 networks:
-  shared:
-    name: shared
+  btc-network:
+    name: btc-network
     external: true
 
 services:
@@ -12,8 +12,7 @@ services:
     depends_on:
       - frankfurter
     networks:
-      - default
-      - shared
+      - btc-network
     environment:
       BTCDATA_PORT: "${DOCKER_BTCDATA_PORT}"
       JDBC_URL: "${DOCKER_JDBC_URL}"
@@ -26,3 +25,5 @@ services:
   frankfurter:
     image: lineofflight/frankfurter
     restart: unless-stopped
+    networks:
+      - btc-network