[fix](trx-frontend-http): compress images and fix SSE heartbeat timing

Resize favicon from 1024x1024 to 64x64 and logo from 1024x1024 to
256x256, reducing total image size from ~3 MB to ~70 KB.

Fix SSE heartbeat race condition where the 10s ping interval competed
with the 8s stale threshold, causing spurious reconnects. Now pings
every 5s server-side, with a 15s stale threshold and 5s check interval
client-side.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -289,11 +289,11 @@ es.onmessage = (evt) => {
 
   esHeartbeat = setInterval(() => {
     const now = Date.now();
-    if (now - lastEventAt > 8000) {
+    if (now - lastEventAt > 15000) {
       es.close();
       connect();
     }
-  }, 4000);
+  }, 5000);
 }
 
 async function postPath(path) {