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/OAuthButton.tsx

@@ -0,0 +1,49 @@
+"use client";
+
+import type { ReactElement } from "react";
+import { Loader2 } from "lucide-react";
+
+export interface OAuthButtonProps {
+  providerName: string;
+  providerId: string;
+  onClick: () => void;
+  isLoading?: boolean;
+  disabled?: boolean;
+}
+
+export function OAuthButton({
+  providerName,
+  onClick,
+  isLoading = false,
+  disabled = false,
+}: OAuthButtonProps): ReactElement {
+  const isDisabled = disabled || isLoading;
+
+  return (
+    <button
+      type="button"
+      role="button"
+      onClick={onClick}
+      disabled={isDisabled}
+      aria-label={isLoading ? "Connecting" : `Continue with ${providerName}`}
+      className={[
+        "w-full inline-flex items-center justify-center gap-2",
+        "rounded-md px-4 py-2 text-base font-medium",
+        "bg-blue-600 text-white hover:bg-blue-700",
+        "transition-colors focus:outline-none focus:ring-2 focus:ring-blue-500",
+        isDisabled ? "opacity-50 pointer-events-none" : "",
+      ]
+        .filter(Boolean)
+        .join(" ")}
+    >
+      {isLoading ? (
+        <>
+          <Loader2 className="h-4 w-4 animate-spin" aria-hidden="true" />
+          <span>Connecting...</span>
+        </>
+      ) : (
+        <span>Continue with {providerName}</span>
+      )}
+    </button>
+  );
+}