[feat](trx-client): add bandplan display config to client settings

Add bandplan_enabled (default: true) and bandplan_region (default:
"iaru_r1") fields to [frontends.http] config section, allowing the
operator to control the initial bandplan display setting from the
server config rather than requiring each browser session to configure
it manually. The server-provided default is applied on first connect
only when the user has no existing localStorage override.

https://claude.ai/code/session_01H7427hzbJepJzkoUJzoDmH
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -3177,6 +3177,22 @@ function render(update) {
   if (typeof update.show_sdr_gain_control === "boolean") {
     if (sdrSettingsRowEl) sdrSettingsRowEl.style.display = update.show_sdr_gain_control ? "" : "none";
   }
+  // Apply server-configured bandplan defaults once, only when the user has not
+  // previously overridden the setting via the UI (localStorage).
+  if (!_bandplanServerDefaultApplied && typeof update.bandplan_enabled === "boolean"
+      && typeof update.bandplan_region === "string") {
+    _bandplanServerDefaultApplied = true;
+    const hasUserOverride = localStorage.getItem(STORAGE_PREFIX + "bandplanRegion") !== null;
+    if (!hasUserOverride) {
+      const region = update.bandplan_enabled ? update.bandplan_region : "off";
+      bandplanRegion = region;
+      saveSetting("bandplanRegion", region);
+      if (bandplanRegionSelect) bandplanRegionSelect.value = region;
+      bandplanSegmentsCache = null;
+      bandplanCacheKey = "";
+      if (lastSpectrumData) scheduleSpectrumDraw();
+    }
+  }
   if (update.filter && sdrAgcEl && typeof update.filter.sdr_agc_enabled === "boolean") {
     sdrAgcEl.checked = update.filter.sdr_agc_enabled;
     updateSdrGainInputState();
@@ -11279,6 +11295,7 @@ if (spectrumCenterRightBtn) {
 let bandplanData = null;
 let bandplanRegion = loadSetting("bandplanRegion", "off");
 let bandplanShowLabels = loadSetting("bandplanLabels", true);
+let _bandplanServerDefaultApplied = false;
 let bandplanSegmentsCache = null;
 let bandplanCacheKey = "";