[feat](trx-frontend-http): move band plan overlay to top of spectrum view

Repositions the bandplan strip from the bottom of the combined spectrum
canvas to the top. Updates HTML element order, CSS bp-webgl absolute
positioning, and WebGL rendering Y coordinates.

https://claude.ai/code/session_015sRhGsk7ggRYoxJANDY72S
Signed-off-by: Claude <noreply@anthropic.com>

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

@@ -119,6 +119,7 @@
       </div>
       <div id="spectrum-panel" style="display:none;">
         <div class="spectrum-wrap">
+          <div id="spectrum-bandplan-strip" aria-label="Band plan allocations"></div>
           <div id="spectrum-bookmark-axis"></div>
           <div id="spectrum-bookmark-side-left" class="spectrum-bookmark-side spectrum-bookmark-side-left" aria-hidden="true"></div>
           <canvas id="spectrum-canvas"></canvas>
@@ -127,7 +128,6 @@
           <div id="spectrum-db-axis" aria-hidden="true"></div>
           <div id="spectrum-bookmark-side-right" class="spectrum-bookmark-side spectrum-bookmark-side-right" aria-hidden="true"></div>
           <div id="spectrum-tooltip"></div>
-          <div id="spectrum-bandplan-strip" aria-label="Band plan allocations"></div>
           <canvas id="spectrum-waterfall-canvas" style="display:none;"></canvas>
           <div id="spectrum-freq-axis">
             <button id="spectrum-center-left-btn" class="spectrum-edge-shift spectrum-edge-shift-left" type="button" aria-label="Shift spectrum center left">&lsaquo;</button>