feat(#415): theme fix, AuthDivider, SessionExpiryWarning components

- AUTH-014: Fix theme storage key (jarvis-theme -> mosaic-theme)
- AUTH-016: Create AuthDivider component with customizable text
- AUTH-019: Create SessionExpiryWarning floating banner (PDA-friendly, blue)
- Fix lint errors in LoginForm, OAuthButton from parallel agents
- Sync pnpm-lock.yaml for recharts dependency

Refs #415

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/components/auth/AuthDivider.tsx

@@ -0,0 +1,18 @@
+interface AuthDividerProps {
+  text?: string;
+}
+
+export function AuthDivider({
+  text = "or continue with email",
+}: AuthDividerProps): React.ReactElement {
+  return (
+    <div className="relative my-6">
+      <div className="absolute inset-0 flex items-center">
+        <span className="w-full border-t border-slate-200" />
+      </div>
+      <div className="relative flex justify-center text-xs uppercase">
+        <span className="bg-white px-2 text-slate-500">{text}</span>
+      </div>
+    </div>
+  );
+}