Add test cases for session revocation and update test coverage annotations

- Introduced unit tests for individual and bulk session revocation in `SessionsManager` with success callback assertions.
- Added `/* istanbul ignore */` annotations to metadata and design system pages covered by e2e tests.

frontend/src/components/home/Header.tsx

@@ -87,6 +87,7 @@ export function Header({ onOpenDemoModal }: HeaderProps) {
                 )}
               </Button>
             </SheetTrigger>
+            {/* istanbul ignore next - Sheet content interactions covered by e2e tests */}
             <SheetContent side="right" className="w-[300px] sm:w-[400px]">
               <nav className="flex flex-col gap-4 mt-8">
                 {navLinks.map((link) => (