[feat](trx-frontend-http): make auto-squelch a toggle, default to Off

The Auto button now toggles between Off and Auto states. Default is Off.
First click sets squelch to noise floor + 6 dB; second click resets to
Open (0%). Button shows active state with green highlight when engaged.

https://claude.ai/code/session_01TDQyrZiPKfWGATVWPsLmHT
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -1286,6 +1286,10 @@ small { color: var(--text-muted); }
   border-radius: 3px;
   cursor: pointer;
 }
+.sql-auto-btn.active {
+  background: var(--accent-green);
+  color: #000;
+}
 .vol-slider {
   -webkit-appearance: none;
   appearance: none;