Initial commit: btcdata — BTC data backend service

Split from btcprice monolith. Owns DB, migrations, Binance WebSocket,
Kraken OHLC pollers, and exposes a JSON API with SSE price stream.

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

env/prod/resources/logback.xml

@@ -0,0 +1,14 @@
+<configuration>
+  <statusListener class="ch.qos.logback.core.status.NopStatusListener" />
+  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+    </encoder>
+  </appender>
+  <root level="INFO">
+    <appender-ref ref="STDOUT" />
+  </root>
+  <logger name="org.eclipse.jetty" level="WARN" />
+  <logger name="io.undertow" level="WARN" />
+  <logger name="org.xnio" level="WARN" />
+</configuration>