feat: replace unified loading approach with global loading provider and refactor loading handling across components

- Introduced GlobalLoadingProvider to manage a consistent loading overlay across the application.
- Replaced existing loading implementations with useGlobalLoadingEffect hook for better control and to prevent animation resets.
- Updated components such as LoginPage, AuthCallbackPage, and DashboardLayout to utilize the new global loading mechanism.
- Removed UnifiedLoadingScreen component to streamline loading management and enhance user experience.

surfsense_web/components/TokenHandler.tsx

@@ -3,7 +3,7 @@
 import { useSearchParams } from "next/navigation";
 import { useTranslations } from "next-intl";
 import { useEffect } from "react";
-import { UnifiedLoadingScreen } from "@/components/ui/unified-loading-screen";
+import { useGlobalLoadingEffect } from "@/hooks/use-global-loading";
 import { getAndClearRedirectPath, setBearerToken } from "@/lib/auth-utils";
 import { trackLoginSuccess } from "@/lib/posthog/events";
 
@@ -30,6 +30,9 @@ const TokenHandler = ({
 	const t = useTranslations("auth");
 	const searchParams = useSearchParams();
 
+	// Always show loading for this component - spinner animation won't reset
+	useGlobalLoadingEffect(true, t("processing_authentication"), "default");
+
 	useEffect(() => {
 		// Only run on client-side
 		if (typeof window === "undefined") return;
@@ -69,9 +72,8 @@ const TokenHandler = ({
 		}
 	}, [searchParams, tokenParamName, storageKey, redirectPath]);
 
-	return (
-		<UnifiedLoadingScreen variant="default" message={t("processing_authentication")} />
-	);
+	// Return null - the global provider handles the loading UI
+	return null;
 };
 
 export default TokenHandler;