Proxy btcdata WebSocket through btcprice for remote access

Browser can't reach the LAN-only btcdata WebSocket when accessing
btcprice remotely (Tailscale/Cloudflare Tunnel). Add a /ws/price
proxy route that relays btcdata frames to the browser so only
btcprice needs to be reachable.

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

resources/system.edn

@@ -36,5 +36,8 @@
  {:base-path "/api"}
 
  :reitit.routes/ui
+ {:base-path ""}
+
+ :reitit.routes/ws-proxy
  {:base-path   ""
   :btcdata-url #or [#env BTCDATA_URL "http://localhost:4100"]}}