[fix](trx-frontend-http): use green color for active header play button

The .audio-active state was using --accent-green which is actually
orange (#c24b1a). Match the regular play button's hardcoded #00d17f
green so the header button visually matches.

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

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

@@ -1046,8 +1046,8 @@ small { color: var(--text-muted); }
   height: 100%;
 }
 .header-audio-btn.audio-active {
-  color: var(--accent-green);
-  border-color: var(--accent-green);
+  color: #00d17f;
+  border-color: #00d17f;
 }
 .header-rig-switch {
   display: flex;