[feat](trx-frontend-http): migrate frontend canvas rendering to WebGL

Replace Canvas2D rendering in spectrum, overview, signal overlay, and CW tone picker with a shared WebGL renderer and wire the new asset into frontend HTTP routes.\n\nCo-authored-by: OpenAI Codex <codex@openai.com>

Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -2182,6 +2182,28 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   cursor: crosshair;
   touch-action: none;
 }
+#spectrum-db-axis {
+  position: absolute;
+  top: 0;
+  left: 0;
+  width: 3rem;
+  height: var(--spectrum-plot-height);
+  pointer-events: none;
+  z-index: 7;
+}
+#spectrum-db-axis span {
+  position: absolute;
+  left: 0.22rem;
+  transform: translateY(-50%);
+  font-size: 0.62rem;
+  line-height: 1;
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
+  color: var(--text-muted);
+  font-weight: 700;
+  letter-spacing: 0.01em;
+  text-shadow: 0 1px 2px color-mix(in srgb, var(--bg) 65%, transparent);
+  white-space: nowrap;
+}
 .spectrum-edge-shift {
   position: absolute;
   top: calc((var(--spectrum-plot-height) - var(--overview-plot-height)) / 2);