[feat](trx-frontend-http): make the SQL label the squelch switch

Clicking SQL turns the squelch on and off.  The label and the button
beside it said the same thing twice — one naming the control, the other
reading "On" or "Off" — where the name itself is the obvious target, and
the dot already carries the state: grey when off, green while the gate
passes, amber while it holds.

The pressed state is on the label, so the switch reads the same to a
screen reader as it looks.

Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/spectrum-layout.mjs

@@ -144,12 +144,12 @@ try {
       shown: getComputedStyle(line).display !== "none",
       db: Number(document.getElementById("sdr-squelch-db").value),
       label: Number(document.getElementById("spectrum-squelch-label").textContent),
-      toggle: document.getElementById("sdr-squelch-toggle").textContent,
+      toggle: document.getElementById("sdr-squelch-toggle").getAttribute("aria-pressed"),
       top: Math.round(line.getBoundingClientRect().top),
     };
   });
   assert.equal(squelchOn.shown, true, "the threshold line did not appear with the squelch on");
-  assert.equal(squelchOn.toggle, "On", "the toggle did not follow the squelch state");
+  assert.equal(squelchOn.toggle, "true", "the SQL switch did not follow the squelch state");
   assert.equal(squelchOn.label, squelchOn.db, "the line and the readout disagree on the threshold");
 
   // Dragging the line down lowers the threshold and tells the server.