Switch price updates from HTMX polling to SSE

Replace 2s polling with Server-Sent Events for instant price updates.
Write directly to Undertow exchange output stream to ensure proper
flushing, since the Ring adapter buffers InputStream bodies.

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

resources/system.edn

@@ -51,7 +51,8 @@
 
  :reitit.routes/ui
  {:base-path ""
-  :query-fn  #ig/ref :db.sql/query-fn}
+  :query-fn  #ig/ref :db.sql/query-fn
+  :binance   #ig/ref :ws/binance}
 
  :ws/binance
  {:query-fn #ig/ref :db.sql/query-fn