refactor(frontend): finish design-system migration — chatbot, a11y, lint

- Rewrite chatbot container + panel to new surface/signal/ink tokens
  (was still on dead glass/text-primary tokens -> wrong colors)
- loading-skeleton: glass -> surface-2
- Fix a11y: SVG charts role=img+aria-label, audio aria-label,
  message-entry as real <button>, tooltip biome-ignore (intentional)
- Type messages/page initialPage (noImplicitAny)
- tsc clean, next build green, biome 0 errors

services/frontend/src/components/shared/loading-skeleton.tsx

@@ -21,7 +21,7 @@ export function LoadingSkeleton({
     <div
       key={i}
       className={cn(
-        "glass rounded-[var(--radius-card)] overflow-hidden",
+        "surface-2 overflow-hidden",
         height,
         width,
         className,