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/app/(dashboard)/messages/page.tsx

@@ -2,7 +2,7 @@
  * Messages — Server Component.
  * Reads URL guild/channel/selected/tab on the server; seeds first page SSR.
  */
-import { getMessages } from "@/lib/api/server";
+import { getMessages, type MessagePageResult } from "@/lib/api/server";
 import MessagesView from "./view";
 
 export default async function MessagesPage({
@@ -19,7 +19,7 @@ export default async function MessagesPage({
       ? (sp.tab as "all" | "images" | "review")
       : "all";
 
-  let initialPage;
+  let initialPage: MessagePageResult | undefined;
   if (guild) {
     initialPage = await getMessages(guild, channel || undefined).catch(
       () => undefined,

services/frontend/src/app/(dashboard)/recordings/view.tsx

@@ -149,7 +149,13 @@ function PreviewDialog({
         <div className="display text-lg text-[var(--color-signal)]">
           {recording.filename}
         </div>
-        <audio controls src={recording.download_url ?? ""} className="w-full" />
+        {/* biome-ignore lint/a11y/useMediaCaption: voice recordings are uncaptioned audio previews — no transcript available */}
+        <audio
+          controls
+          src={recording.download_url ?? ""}
+          aria-label={`Audio recording: ${recording.filename}`}
+          className="w-full"
+        />
         <div className="mono text-xs text-[var(--color-ink-soft)]">
           {(recording.size_bytes / 1024).toFixed(0)} KB ·{" "}
           {recording.upload_status}