[refactor](trx-frontend-http): simplify auto-squelch to single-click action

Revert toggle approach back to a simple button: click sets squelch to
noise floor + 6 dB when spectrum data is available, or Off otherwise.

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

@@ -1286,10 +1286,6 @@ 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;