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>

CLAUDE.md

@@ -38,7 +38,7 @@ btcprice's docker-compose includes btcdata via `include: ../btcdata/docker-compo
 - **Routing:** Reitit
 - **Templates:** Hiccup + HTMX (WebSocket extension)
 - **Styling:** Tailwind CSS v4
-- **Data backend:** btcdata (separate service at BTCDATA_URL, default http://192.168.50.42:4100)
+- **Data backend:** btcdata (separate service at BTCDATA_URL, default http://localhost:4100)
 - **No database** — all data comes from btcdata
 
 ## Source Layout
@@ -59,5 +59,6 @@ src/clj/pmagnus/btcprice/
     └── routes/
         ├── api.clj       # /api routes (JSON)
         ├── ui.clj        # UI routes (HTML + HTMX WebSocket)
+        ├── ws_proxy.clj  # WebSocket proxy to btcdata
         └── utils.clj     # Route utilities
 ```