fix: refactor logout to use synchronous flow with full page redirect

- Rewrite logout() from async to synchronous to prevent React re-renders with stale state
- Replace router.push('/login') with redirectToLogin() (window.location.replace) in all page auth guards for reliable navigation in Edge/Safari
- Add performFullLogout() helper that clears auth state, feature stores, and localStorage
- Fix persist middleware partialize to return {} when not authenticated, preventing state resurrection
- Use keepalive fetch for background cookie/token cleanup so redirect fires immediately
- Remove unused useRouter imports from page.tsx and contacts/page.tsx
- Simplify all page logout handlers to directly call logout()

Fixes #63

components/layout/account-switcher.tsx

@@ -101,15 +101,11 @@ export function AccountSwitcher({ variant = "rail", className }: AccountSwitcher
   const handleLogout = () => {
     setOpen(false);
     logout();
-    if (useAccountStore.getState().accounts.length === 0) {
-      router.push("/login" as never);
-    }
   };
 
   const handleLogoutAll = () => {
     setOpen(false);
     logoutAll();
-    router.push("/login" as never);
   };
 
   const handleSetDefault = (accountId: string) => {