[style](trx-frontend-http): update copyright footer with callsign link

Shorten to "Built by SP2SJG" and link callsign to qrzcq.com.

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/index.html

@@ -106,7 +106,7 @@
       </div>
     </div>
     <div class="footer">
-      <div class="copyright">Built by Stan Grams SP2SJG from <a href="https://haxx.space" target="_blank" rel="noopener">haxx.space</a> — <span id="copyright-year"></span></div>
+      <div class="copyright">Built by <a href="https://www.qrzcq.com/call/SP2SJG" target="_blank" rel="noopener">SP2SJG</a> from <a href="https://haxx.space" target="_blank" rel="noopener">haxx.space</a> — <span id="copyright-year"></span></div>
       <div class="hint" id="power-hint">Connecting…</div>
     </div>
     </div>