Remove duplicate header stats and fix icon rendering

- Remove duplicated message counters from header (keeping output panel stats)
- Remove syncHeaderStats function and its 500ms polling interval
- Fix icon CSS override that caused stroke-based SVGs to render as solid squares

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/css/modes/tscm.css

@@ -1305,7 +1305,6 @@
 .icon svg {
     width: 100%;
     height: 100%;
-    fill: currentColor;
 }
 
 .icon--sm {