fix: Display validation errors from catalog API responses

[jeff-schnitter]

Summary

When the catalog API returns a 400 error with validation violations, the CLI displays generic error messages instead of the actual validation details.

Current Behavior

HTTP Error 400: Unknown error - No details (Request ID: No request ID)

Expected Behavior

The CLI should display the validation violations returned by the API:

{
  "ok": false,
  "violations": [
    {
      "title": "Cortex Entity Relationships",
      "description": "Relationships of type 'geography' from 'united-states' cannot have sources of type 'service'.",
      "violationType": "MUST",
      "ruleLink": "https://docs.cortex.io/",
      "paths": ["/info//x-cortex-relationships"],
      "pointer": "/info//x-cortex-relationships",
      "startLine": 1,
      "endLine": 58
    }
  ]
}

Root Cause

The error handling in cortexapps_cli/cortex_client.py (lines 147-160) expects a specific JSON structure with message, details, and requestId fields, but validation errors use a violations array structure instead.

Proposed Solution

Update the error handling in CortexClient.request() to detect and format violations array responses in addition to the existing error format.