Point citadel btcprice at the local btcdata over btc-network

omarchy is gone, but the citadel deployment still set
BTCDATA_URL=http://192.168.50.42:4102 and ran standalone on its own
compose network. Every request that proxies to btcdata failed with
httpx.ConnectError: All connection attempts failed.

btcdata now runs on citadel too, so attach btcprice to the external
btc-network there and reach it by service name at http://btcdata:4102.
deploy-citadel.sh creates the network on the remote if missing, as
btcdata's own deploy script already does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TRkiLhK5qhkZjP2adxpA3e

docker-compose.citadel.yml

@@ -1,10 +1,18 @@
 # Deployment compose for citadel. Copied to $APP_DIR/docker-compose.yml by
 # deploy-citadel.sh, which also copies .env.citadel to $APP_DIR/.env.
-# Standalone: btcdata is remote, so no btc-network here.
+# btcdata also runs on citadel, so both attach to the external btc-network and
+# btcprice reaches it by service name.
+networks:
+  btc-network:
+    name: btc-network
+    external: true
+
 services:
   btcprice:
     image: btcprice:latest
     restart: unless-stopped
+    networks:
+      - btc-network
     ports:
       - "${BTCPRICE_PORT:-4041}:4040"
     environment: