feat(admin): add dedicated user management page

Extract user management functionality from MembersPage drawer into a
dedicated UserManagementPage at /org/members/:userId. The new page
provides a full-page interface with tabs for user details, security
settings (MFA methods), and access management (OAuth accounts, SSH keys).

This improves code organization by separating concerns and provides
better UX for user administration tasks.

src/App.tsx

@@ -43,6 +43,7 @@ import CLIGuidePage from "@/pages/user/CLIGuidePage";
 // Organization pages
 import OrgOverviewPage from "@/pages/org/OrgOverviewPage";
 import MembersPage from "@/pages/org/MembersPage";
+import UserManagementPage from "@/pages/admin/UserManagementPage";
 import PoliciesPage from "@/pages/org/PoliciesPage";
 import CompliancePage from "@/pages/org/CompliancePage";
 import OrgAuditPage from "@/pages/org/OrgAuditPage";
@@ -198,6 +199,7 @@ function AppRoutes() {
 
           {/* Organization management routes — org admins/owners only */}
           <Route path="/org/members" element={<RequireAdmin><MembersPage /></RequireAdmin>} />
+          <Route path="/org/members/:userId" element={<RequireAdmin><UserManagementPage /></RequireAdmin>} />
           <Route path="/org/departments" element={<RequireAdmin><DepartmentsPage /></RequireAdmin>} />
           <Route path="/org/principals" element={<RequireAdmin><PrincipalsPage /></RequireAdmin>} />
           <Route path="/org/api-keys" element={<RequireAdmin><ApiKeysPage /></RequireAdmin>} />