docs: document BaseUrl override for OpenAPI import in quick ref and skill

Add BaseUrl override example and explanation to both
MDL_QUICK_REFERENCE.md and .claude/skills/mendix/rest-client.md.
The behavior (BaseUrl overrides servers[0].url from the spec) was
already implemented and tested but missing from both doc locations.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: khode-mx

.claude/skills/mendix/rest-client.md

@@ -30,6 +30,12 @@ create or modify rest client CapitalModule.CapitalAPI (
 create or modify rest client PetStoreModule.PetStoreAPI (
   OpenAPI: 'https://petstore3.swagger.io/api/v3/openapi.json'
 );
+
+-- Override the base URL (replaces servers[0].url from the spec)
+create or modify rest client PetStoreModule.PetStoreStaging (
+  OpenAPI: 'https://petstore3.swagger.io/api/v3/openapi.json',
+  BaseUrl: 'https://staging.petstore.example.com/api/v3'
+);
 ```
 
 This generates:
@@ -38,6 +44,8 @@ This generates:
 - Basic auth if the spec declares it at the top level
 - The spec stored inside the document for Studio Pro parity
 
+`BaseUrl` is optional. When omitted, `servers[0].url` from the spec is used. When provided, it overrides that value — useful when the spec points at production but you need to import against staging or a different version.
+
 **Preview without writing:**
 ```sql
 describe contract operation from openapi 'specs/capital.json';

docs/01-project/MDL_QUICK_REFERENCE.md

@@ -611,12 +611,20 @@ create or modify rest client PetStoreModule.PetStoreAPI (
   OpenAPI: 'https://petstore3.swagger.io/api/v3/openapi.json'
 );
 
+-- Override the base URL from the spec (e.g. point at staging instead of prod)
+create or modify rest client PetStoreModule.PetStoreStaging (
+  OpenAPI: 'https://petstore3.swagger.io/api/v3/openapi.json',
+  BaseUrl: 'https://staging.petstore.example.com/api/v3'
+);
+
 -- Preview without writing to the project
 describe contract operation from openapi 'specs/capital.json';
 ```
 
 Operations, path/query parameters, headers, request body, response type, resource groups (from OpenAPI `tags`), and Basic auth are all derived automatically. The spec is stored inside the REST client document for Studio Pro parity.
 
+`BaseUrl` is optional. When omitted, the base URL is taken from `servers[0].url` in the spec. When provided, it overrides that value — useful when the spec points at production but you want to import against a different environment.
+
 ## Published REST Services
 
 | Statement | Syntax | Notes |