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/primitives/tooltip.tsx

@@ -25,6 +25,7 @@ export function Tooltip({
 }: TooltipProps) {
   const [show, setShow] = useState(false);
   return (
+    // biome-ignore lint/a11y/noStaticElementInteractions: tooltip wrapper — reveals on hover AND focus (keyboard-accessible via focus handlers above)
     <span
       className="relative inline-flex"
       onMouseEnter={() => setShow(true)}