fix(ui+backend): sidebar active state + technique status after test deletion

- Sidebar: add `end` prop to child NavLinks so "All Tests" (/tests) is
  only highlighted when exactly on /tests, not on /tests/validated.
- Backend: recalculate technique status_global for all affected techniques
  when tests are deleted via delete_campaign(delete_tests=True), preventing
  stale coverage metrics on the dashboard.

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

frontend/src/components/Sidebar.tsx

@@ -82,6 +82,7 @@ function SidebarLink({ item }: { item: NavItem }) {
               <NavLink
                 key={child.to + child.label}
                 to={child.to}
+                end
                 className={({ isActive }) =>
                   `flex items-center gap-3 rounded-lg px-3 py-2 text-sm transition-colors ${
                     isActive