fix: address review findings (body truncation, unused field, whitespace)

Self-review fixes for PR #54:

- Add truncateBody helper to limit error message body length (200 chars)
  Addresses security bot finding about potential information leakage
  in error messages that include upstream response bodies

- Remove unused deployment.ID field from deployment struct
  Now stores just the URL string directly in the deployments map
  Addresses sonnet finding about unused struct field

- Add doc comment noting deployment cache limitation
  Documents that cache is never invalidated, acceptable for CI use case

- Fix trailing whitespace in action.yml aicore-resource-group default

All existing tests pass.

.gitea/actions/review/action.yml

@@ -59,7 +59,7 @@ inputs:
   aicore-resource-group:
     description: 'SAP AI Core resource group (default: default)'
     required: false
-    default: 'default' 
+    default: 'default'
   conventions-file:
     description: 'Path to conventions file in the repo (e.g. CLAUDE.md)'
     required: false