feat(models): define capability schema and readers (#2739)

* feat(models): define capability schema and readers

* fix(models): harden Google catalog probing

Restrict native catalog probing to the Gemini host, keep provider keys out of request URLs, filter non-chat model resources, and preserve the manual refresh default in the built-in Google add flow.

tests/test_admin_device_flow_static.py

@@ -28,6 +28,24 @@ def test_provider_selection_is_inert_and_add_button_starts_device_flow():
     assert "_startProviderDeviceAuth(deviceAuthProvider" in add_block
 
 
+def test_google_add_omits_auto_refresh_mode_for_backend_manual_default():
+    refresh_helper = _between(
+        _ADMIN,
+        "function _modelRefreshModeForApiEndpoint",
+        "function _normalizeBaseUrl",
+    )
+    add_block = _between(
+        _ADMIN,
+        "el('adm-epAddBtn').addEventListener('click'",
+        "async function _startProviderDeviceAuth",
+    )
+
+    assert "generativelanguage.googleapis.com" in refresh_helper
+    assert "return '';" in refresh_helper
+    assert "_modelRefreshModeForApiEndpoint(url, endpointKind)" in add_block
+    assert "if (refreshMode) fd.append('model_refresh_mode', refreshMode)" in add_block
+
+
 def test_device_auth_selection_disables_and_dims_api_test_button():
     form_block = _between(_ADMIN, "function _setApiFormForProvider()", "function _renderPickerMenu()")