[fix](trx-frontend-http): keep layout sections togglable

A layout seeds the collapsible sections; it should not hold them there.
applyLayout writes the disclosure state of the advanced, audio and
scheduler sections, and it runs far more often than a layout change:
render() calls applyRigList() for every SSE frame carrying `remotes`,
which calls setActiveRig() unconditionally, which re-applies the layout.

An operator who expanded a section that the selected layout collapses by
default therefore had it shut again within about a second, which read as
the section being locked by the layout — most visibly the scheduler under
Compact.

Write the section state only when the layout actually changes, or the
first time each section appears in the DOM, since the advanced controls
are constructed after the first applyLayout call.  Switching layout still
reseeds every section, so choosing a layout keeps meaning "give me these
defaults".

Verified in Chromium: with Compact selected, activating the scheduler
summary opens the section and it survives both a rig-state refresh and a
repeated applyLayout, while selecting Full still reseeds it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GdyUjuXejCEfiub675z6cz
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/ui-core.test.mjs

@@ -143,4 +143,31 @@ ui.applyLayout("digital");
 assert.equal(document.body.dataset.operatorLayout, "compact");
 assert.equal(localStorage.getItem("trxOperatorLayout:rig-b"), "compact");
 
+// A layout seeds the collapsible sections but must not hold them there:
+// applyLayout runs on every rig-state refresh, so an operator who expands a
+// section a layout collapses by default had it shut again about once a second.
+const schedulerSection = new Element("details", document);
+schedulerSection.id = "scheduler-controls";
+const audioSection = new Element("details", document);
+audioSection.id = "audio-controls";
+
+ui.setActiveRig("rig-c");
+ui.applyLayout("compact");
+assert.equal(schedulerSection.open, false, "compact seeds the scheduler section closed");
+
+schedulerSection.open = true;             // operator expands it
+ui.applyLayout("compact");                // the next rig-state refresh
+assert.equal(schedulerSection.open, true, "re-applying the same layout leaves sections alone");
+ui.setActiveRig("rig-c");
+assert.equal(schedulerSection.open, true, "a rig-state refresh leaves sections alone");
+
+// Choosing a different layout is an explicit request for its defaults.
+ui.applyLayout("full");
+assert.equal(schedulerSection.open, true, "full seeds the scheduler section open");
+assert.equal(audioSection.open, true, "full seeds the audio section open");
+audioSection.open = false;
+ui.applyLayout("compact");
+assert.equal(audioSection.open, false, "compact seeds the audio section closed");
+assert.equal(schedulerSection.open, false, "switching layout reseeds every section");
+
 console.log("ui-core component tests passed");