[fix](trx-frontend-http): show map loading message, sync active rig marker, align recorder actions with bookmarks

- Display "Loading map…" placeholder on first map tab click while
  map-core.js is still loading; hide it once the module initializes.
- Sync receiver marker highlight when switching rigs so the map
  reflects the currently active rig immediately.
- Add "Actions" header to recorder files table and match button
  sizing to bookmarks table style.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -977,6 +977,7 @@
       </div>
     </div>
     <div id="tab-map" class="tab-panel" data-tab="map" style="display:none;">
+      <div id="map-loading" class="map-loading-msg">Loading map&hellip;</div>
       <template id="tmpl-map">
       <div id="map-stage">
         <div class="map-overlay-panel">