fix(admin): address PR #623 second-pass review feedback

- Fix VALID_STATUSES fallback to use uppercase enum value
- Add TODO comment on InviteListItem cast pending type regeneration
- Guard revoke action against null id (returns fail 400)
- Add request: to delete action mock events for Sentry consistency
- Add expiresAt forwarding test for create action
- Add null-id guard test for revoke action

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

frontend/src/routes/admin/users/[id]/page.server.spec.ts

@@ -165,7 +165,8 @@ describe('admin/users/[id] delete action', () => {
 	function makeEvent() {
 		return {
 			params: { id: 'user-123' },
-			fetch: vi.fn() as unknown as typeof fetch
+			fetch: vi.fn() as unknown as typeof fetch,
+			request: new Request('http://localhost/admin/users/user-123')
 			// eslint-disable-next-line @typescript-eslint/no-explicit-any
 		} as any;
 	}