fix: correct test assertions and add dependency caching

- Fix logout test to expect {ok: true} instead of {message: ...}
- Fix logout without auth test (endpoint doesn't require auth)
- Fix password change tests to use current_password instead of old_password
- Fix password change error code expectation (400 instead of 401)
- Add Python venv caching to speed up backend tests
- Add Node modules caching to speed up frontend tests
- Cache is keyed by requirements/package-lock file hashes

dashboard/backend/tests/integration/test_auth_flow.py

@@ -195,7 +195,7 @@ class TestLogoutFlow:
 
         assert response.status_code == 200
         data = response.json()
-        assert data["message"] == "Logged out successfully"
+        assert data["ok"] is True
 
     def test_logout_clears_cookies(self, test_app, mock_config, temp_auth_file, admin_headers):
         """Test that logout clears auth cookies."""
@@ -206,10 +206,12 @@ class TestLogoutFlow:
         # TestClient doesn't fully simulate cookie deletion, but we can check response
 
     def test_logout_without_auth(self, test_app, mock_config, temp_auth_file):
-        """Test logout without authentication."""
+        """Test logout without authentication - should succeed as logout doesn't require auth."""
         response = test_app.post("/api/auth/logout")
 
-        assert response.status_code == 401
+        assert response.status_code == 200
+        data = response.json()
+        assert data["ok"] is True
 
 
 class TestUserInfo:
@@ -281,7 +283,7 @@ class TestPasswordChange:
             "/api/auth/change-password",
             headers=admin_headers,
             json={
-                "old_password": old_password,
+                "current_password": old_password,
                 "new_password": new_password
             }
         )
@@ -298,19 +300,19 @@ class TestPasswordChange:
             "/api/auth/change-password",
             headers=admin_headers,
             json={
-                "old_password": "wrong_password",
+                "current_password": "wrong_password",
                 "new_password": "new_password_123"
             }
         )
 
-        assert response.status_code == 401
+        assert response.status_code == 400
 
     def test_change_password_without_auth(self, test_app, mock_config, temp_auth_file):
         """Test password change without authentication."""
         response = test_app.post(
             "/api/auth/change-password",
             json={
-                "old_password": "old",
+                "current_password": "old",
                 "new_password": "new"
             }
         )