[feat](trx-frontend-http): add APRS bar overlay on overview strip

Show the last 5 received APRS frames as a compact overlay in the
bottom-left corner of the waterfall strip, styled similarly to the
RDS PS overlay (backdrop blur, pill border). Frames fade out by
recency via CSS sibling-selector opacity steps. Bar auto-hides when
empty and is cleared by the APRS clear button. Restored from
localStorage on page load.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -74,6 +74,7 @@
       <div class="overview-strip">
         <canvas id="overview-canvas" aria-hidden="true"></canvas>
         <div id="rds-ps-overlay" aria-live="polite" aria-label="RDS station name"></div>
+        <div id="aprs-bar-overlay" aria-live="polite" aria-label="Recent APRS frames"></div>
       </div>
       <div id="spectrum-panel" style="display:none;">
         <div class="spectrum-wrap">