[fix](trx-frontend-http): show one rig at a time on the digital modes page

A client connected to several rigs decodes all of them at once, and the
decode stream carries every rig's traffic to every browser.  The decoder
panels listed all of it: a station a background rig copied on another band
appeared in the APRS list next to the selected rig's, the vessel counts and
the "latest seen" lines counted both, the status lines said "Receiving"
because some other rig was, and the CW pane interleaved two rigs into one
stream of text that read as neither.

The page is about the rig the operator selected — the one whose spectrum is
on screen and whose audio is playing — so each panel now shows what that rig
heard: rows, counts, latest-seen, status, the live picture a WEFAX or SSTV
frame is painting, and the CW pane.

Nothing is dropped on the way in.  The map is the whole station's view, has
its own rig filter, and would empty out if the plugins stopped feeding it, so
the histories still hold every rig and the map still plots them.  That also
means a switch loses nothing: the runtime gained a rerender hook, which the
rig switch calls, and switching back brings the other rig's traffic up again.
The CW pane is the exception — a running stream of text cannot be unpicked
after the fact — so it starts empty on the rig switched to.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SyX26FCpMQxiBoC7r5K1A7
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/decode-flow.mjs

@@ -22,9 +22,9 @@ const BEACON = {
   packet_type: "position", crc_ok: true, lat: 54.35, lon: 18.65,
   symbol_table: "/", symbol_code: ">", rig_id: "rig-a",
 };
-// A second rig listening in the background, on its own band. Its traffic
-// belongs in the panels, which aggregate every rig, but not in the mini view,
-// which captions the spectrum of the rig on screen.
+// A second rig listening in the background, on its own band. Both pages
+// describe the rig on screen, so its traffic belongs in neither the panel nor
+// the mini view — only on the map, which shows the whole station.
 const OTHER_RIG_VESSEL = {
   ...VESSEL, mmsi: 244660001, vessel_name: "ELDERBERRY", callsign: "PBTY",
   lat: 51.92, lon: 4.48, rig_id: "rig-b",
@@ -51,12 +51,13 @@ try {
     aisStatus: document.getElementById("ais-status")?.textContent ?? "",
     aprsStatus: document.getElementById("aprs-status")?.textContent ?? "",
     otherRig: document.getElementById("ais-messages")?.textContent.includes("ELDERBERRY") ?? false,
+    aisRows: document.getElementById("ais-messages")?.children.length ?? 0,
     mapLoaded: !!window.trx.modules.map,
   }));
   assert.equal(panels.mapLoaded, false, "the map module was loaded, so this proves nothing");
   assert.ok(panels.ais > 0, `the AIS panel is empty (status: ${panels.aisStatus})`);
   assert.ok(panels.aprs > 0, `the APRS panel is empty (status: ${panels.aprsStatus})`);
-  assert.equal(panels.otherRig, true, "the AIS panel dropped the background rig's vessel");
+  assert.equal(panels.otherRig, false, "the AIS panel listed a background rig's vessel");
 
   // The mini view rides over the waterfall on the radio page.
   await page.locator('.tab[data-tab="main"]').click();
@@ -102,8 +103,11 @@ try {
       : Object.keys(collection ?? {}).length);
     return { ais: size(map?.aisMarkers), stations: size(map?.stationMarkers) };
   });
-  assert.ok(markers.ais > 0, "the vessel never reached the map");
   assert.ok(markers.stations > 0, "the APRS station never reached the map");
+  // The map is the whole station's view — the one place a background rig's
+  // traffic belongs — so both vessels are on it even though the panel and the
+  // mini view show only the selected rig's.
+  assert.equal(markers.ais, 2, `${markers.ais} of 2 vessels reached the map`);
 
   assert.deepEqual(runtimeErrors, []);
 } finally {