feat(frontend): restyle ThothII to the Omics Portal (GSD) design system

Adopt the portal's design language so the app embeds seamlessly into its
header/sidebar chrome later:
- Token layer rewritten as raw OKLCH triplets (the previous oklch()-wrapped
  vars produced invalid colors; the UI was effectively unstyled). Values mirror
  GSD: Manrope + Fraunces fonts, #cb333b red brand, warm off-white surfaces,
  pill buttons, brand focus rings. Dark tokens follow .dark or the portal's
  [data-bs-theme=dark].
- Layout: no left sidebar, no header (the portal supplies them). Conversation
  column flush-left with a slim F1-F8 phase strip; session rail moved to the
  RIGHT, mirroring the portal's left sidebar (red section label, red-tint active
  item). Editorial empty state.
- Transcript component now actually renders the streamed assistant turns (the
  store accumulated them but nothing displayed them). Toaster mounted for errors
  (matchMedia polyfill added to the jsdom test setup).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/Transcript.tsx

@@ -0,0 +1,28 @@
+// frontend/src/shell/Transcript.tsx
+import ReactMarkdown from "react-markdown";
+import remarkGfm from "remark-gfm";
+import { useSessionStore } from "../store/sessionStore";
+
+/**
+ * Renders the streamed assistant conversation. The store accumulates assistant
+ * text deltas in `transcript`; this is the surface that shows them.
+ */
+export function Transcript() {
+  const transcript = useSessionStore((s) => s.transcript);
+  if (transcript.length === 0) return null;
+
+  return (
+    <div className="flex flex-col gap-6">
+      {transcript.map((entry, i) => (
+        <article key={i} className="flex flex-col gap-1.5">
+          <span className="font-heading text-xs font-semibold uppercase tracking-[0.12em] text-primary/80">
+            ThothII
+          </span>
+          <div className="thot-prose">
+            <ReactMarkdown remarkPlugins={[remarkGfm]}>{entry.text}</ReactMarkdown>
+          </div>
+        </article>
+      ))}
+    </div>
+  );
+}