Add core auth hook and logout handler stubs

Introduces a stub implementation for the core useAuth hook and a core logout handler (useAccountLogout) for open-source builds, allowing proprietary/desktop builds to override via path resolution. Also updates FirstLoginModal to pass confirmPassword to changePasswordOnLogin.

Author: Ludy87

frontend/src/core/auth/UseSession.tsx

@@ -0,0 +1,23 @@
+export interface AuthContextType {
+  session: null;
+  user: null;
+  loading: boolean;
+  error: Error | null;
+  signOut: () => Promise<void>;
+  refreshSession: () => Promise<void>;
+}
+
+/**
+ * Core (open-source) auth hook stub.
+ * Proprietary/desktop builds override this file via path resolution.
+ */
+export function useAuth(): AuthContextType {
+  return {
+    session: null,
+    user: null,
+    loading: false,
+    error: null,
+    signOut: async () => {},
+    refreshSession: async () => {},
+  };
+}

frontend/src/core/components/shared/FirstLoginModal.tsx

@@ -52,7 +52,7 @@ export default function FirstLoginModal({ opened, onPasswordChanged, username }:
       setLoading(true);
       setError('');
 
-      await accountService.changePasswordOnLogin(currentPassword, newPassword);
+      await accountService.changePasswordOnLogin(currentPassword, newPassword, confirmPassword);
 
       alert({
         alertType: 'success',

frontend/src/core/extensions/accountLogout.ts

@@ -0,0 +1,20 @@
+type SignOutFn = () => Promise<void>;
+
+interface AccountLogoutDeps {
+  signOut: SignOutFn;
+  redirectToLogin: () => void;
+}
+
+/**
+ * Core (open-source) logout handler: sign out and redirect to /login.
+ * Proprietary/desktop builds override this file via path resolution.
+ */
+export function useAccountLogout() {
+  return async ({ signOut, redirectToLogin }: AccountLogoutDeps): Promise<void> => {
+    try {
+      await signOut();
+    } finally {
+      redirectToLogin();
+    }
+  };
+}