Add user password change functionality

Introduced a backend API endpoint for changing user passwords with validation. Added a new "User Settings" page in the frontend to allow users to update their passwords, including a matching UI update for navigation and styles.

frontend/src/App.jsx

@@ -9,6 +9,7 @@ import { QueryInsightsPage } from "./pages/QueryInsightsPage";
 import { AlertsPage } from "./pages/AlertsPage";
 import { AdminUsersPage } from "./pages/AdminUsersPage";
 import { ServiceInfoPage } from "./pages/ServiceInfoPage";
+import { UserSettingsPage } from "./pages/UserSettingsPage";
 
 function Protected({ children }) {
   const { tokens } = useAuth();
@@ -102,6 +103,9 @@ function Layout({ children }) {
           </div>
           <div>{me?.email}</div>
           <div className="role">{me?.role}</div>
+          <NavLink to="/user-settings" className={({ isActive }) => `profile-btn${isActive ? " active" : ""}`}>
+            User Settings
+          </NavLink>
           <button className="logout-btn" onClick={logout}>Logout</button>
         </div>
       </aside>
@@ -163,6 +167,7 @@ export function App() {
                 <Route path="/query-insights" element={<QueryInsightsPage />} />
                 <Route path="/alerts" element={<AlertsPage />} />
                 <Route path="/service-info" element={<ServiceInfoPage />} />
+                <Route path="/user-settings" element={<UserSettingsPage />} />
                 <Route path="/admin/users" element={<AdminUsersPage />} />
               </Routes>
             </Layout>