Bug: connectivity check blocks adding models in tenant resource management

Bug Report

Describe the bug

In Tenant Resource Management → Models → Add custom model, the connectivity pre-check always reports the model as unavailable for a brand-new model that has not been saved yet, which blocks adding the model.

Steps to reproduce

1. Open Tenant Resource Management, select a tenant
2. Go to Models → Add custom model
3. Fill in base_url / api_key / model_name
4. Click connectivity test

Expected behavior

Connectivity test should verify the raw model config (base_url + api_key + model_name) and return available when the endpoint is reachable, without requiring the model to already exist in the database.

Actual behavior

The check always reports unavailable / blocks save.

Root cause

ModelAddDialog.handleVerifyConnectivity routes the manage flow (tenantId present) through checkManageTenantModelConnectivity → POST /model/manage/healthcheck, which looks up an already-persisted model by display_name + tenant_id. For a new model that lookup fails, so the check always fails.

Environment

• Affected path: tenant resource management (manage flow)
• Self-service add model path is unaffected (already uses /model/temporary_healthcheck)

Start at ModelAddDialog.handleVerifyConnectivity and trace the manage flow through checkManageTenantModelConnectivity to POST /model/manage/healthcheck. Compare it with the self-service /model/temporary_healthcheck path and inspect how the new model's raw base_url, api_key, and model_name are handled. Done means a new manage-flow model can pass connectivity verification without an existing database record.