Split data layer into btcdata service

Remove DB, Binance WebSocket, and Kraken pollers from btcprice.
UI now uses vanilla EventSource connecting to btcdata for live
price updates. btcprice is now a pure UI service with no database.

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

docker-compose.yml

@@ -1,10 +1,22 @@
 services:
+  btcdata:
+    build: ../btcdata
+    restart: unless-stopped
+    ports:
+      - "4100:4100"
+    environment:
+      BTCDATA_PORT: "4100"
+      JDBC_URL: "jdbc:postgresql://postgres:5432/btcprod?user=postgres&password=ratata,123"
+      CORS_ORIGIN: "http://localhost:4040"
+    extra_hosts:
+      - "postgres:host-gateway"
+
   app:
     build: .
     restart: unless-stopped
     ports:
       - "4040:4040"
     environment:
-      JDBC_URL: "jdbc:postgresql://postgres:5432/btcprod?user=postgres&password=ratata,123"
-    extra_hosts:
-      - "postgres:host-gateway"
+      BTCDATA_URL: "http://btcdata:4100"
+    depends_on:
+      - btcdata