fix(ui): render Z.AI API Key and API Base on the credential form

The Add Credential provider list comes from the UI enum, so Z.AI (Zhipu AI)
already appears. GET /public/providers/fields reads provider_create_fields.json,
which had 117 rows and none with litellm_provider=zai, so the form rendered no
fields. Add Model uses that same catalog and never listed Z.AI.

Add the missing catalog row (required api_key, optional api_base) and a
regression on TestZAIDashboardRegistration. Revert-check: the new test fails
with assert 0 == 1 when the row is removed.

litellm/proxy/public_endpoints/provider_create_fields.json

@@ -3414,6 +3414,34 @@
     ],
     "default_model_placeholder": "gpt-3.5-turbo"
   },
+  {
+    "provider": "ZAI",
+    "provider_display_name": "Z.AI (Zhipu AI)",
+    "litellm_provider": "zai",
+    "credential_fields": [
+      {
+        "key": "api_base",
+        "label": "API Base",
+        "placeholder": "https://api.z.ai/api/paas/v4",
+        "tooltip": null,
+        "required": false,
+        "field_type": "text",
+        "options": null,
+        "default_value": null
+      },
+      {
+        "key": "api_key",
+        "label": "API Key",
+        "placeholder": null,
+        "tooltip": null,
+        "required": true,
+        "field_type": "password",
+        "options": null,
+        "default_value": null
+      }
+    ],
+    "default_model_placeholder": "zai/glm-4.5"
+  },
   {
     "provider": "CURSOR",
     "provider_display_name": "Cursor",

tests/test_litellm/llms/zai/test_zai_provider.py

@@ -172,3 +172,29 @@ def test_zai_sync_completion(respx_mock, zai_response, monkeypatch):
 
     assert response.choices[0].message.content == "Hello! How can I help you today?"
     assert response.usage.total_tokens == 25
+
+
+class TestZAIDashboardRegistration:
+    @staticmethod
+    def _provider_create_fields():
+        from pathlib import Path
+
+        path = Path(litellm.__file__).parent / "proxy" / "public_endpoints" / "provider_create_fields.json"
+        with open(path) as f:
+            return json.load(f)
+
+    def test_zai_is_selectable_in_the_add_model_form(self):
+        entries = [e for e in self._provider_create_fields() if e["litellm_provider"] == "zai"]
+        assert len(entries) == 1, "zai must appear exactly once in provider_create_fields.json"
+
+        entry = entries[0]
+        assert entry["provider"] == "ZAI"
+        assert entry["provider_display_name"] == "Z.AI (Zhipu AI)"
+        assert entry["default_model_placeholder"].startswith("zai/")
+
+        fields = {f["key"]: f for f in entry["credential_fields"]}
+        assert fields["api_key"]["required"] is True
+        assert fields["api_key"]["field_type"] == "password"
+        assert fields["api_base"]["required"] is False
+        assert fields["api_base"]["field_type"] == "text"
+        assert fields["api_base"]["placeholder"] == "https://api.z.ai/api/paas/v4"