feat(frontend): CentralStatus + ModelActivityPanel components

frontend/src/shell/ModelActivityPanel.tsx

@@ -0,0 +1,21 @@
+import { X } from "lucide-react";
+import { Transcript } from "./Transcript";
+import { Button } from "../components/ui/button";
+
+/** Left drawer showing the active session's streamed model text ("model activity"),
+ *  opened on demand from the work-in-progress icon. */
+export function ModelActivityPanel({ onClose }: { onClose: () => void }) {
+  return (
+    <aside className="flex w-[380px] shrink-0 flex-col border-r border-border bg-sidebar">
+      <div className="flex items-center justify-between border-b border-border/70 px-4 py-3">
+        <h2 className="font-heading text-sm font-semibold text-foreground">Model activity</h2>
+        <Button size="icon-sm" variant="ghost" aria-label="Close model activity" onClick={onClose}>
+          <X className="size-4" />
+        </Button>
+      </div>
+      <div className="flex-1 overflow-y-auto px-4 py-4">
+        <Transcript />
+      </div>
+    </aside>
+  );
+}