fix: Revert region default change, keep SKIP_AUTH fix

- Reverted IBM_CLOUD_REGION default back to us-south
- User can set IBM_CLOUD_REGION variable to 'ca-tor' to use ca.icr.io
- Kept SKIP_AUTH default='false' fix
- Kept Dockerfile.backend fix for CPU-only PyTorch

The workflow already properly maps ca-tor → ca to use ca.icr.io.
To use ca.icr.io: Set GitHub variable IBM_CLOUD_REGION='ca-tor'

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: manavgup

.github/workflows/deploy_complete_app.yml

@@ -86,7 +86,7 @@ env:
   PROJECT_NAME: rag-modulo-${{ inputs.environment || 'dev' }}
   BACKEND_APP_NAME: ${{ vars.BACKEND_APP_NAME || 'rag-modulo-backend' }}
   FRONTEND_APP_NAME: ${{ vars.FRONTEND_APP_NAME || 'rag-modulo-frontend' }}
-  IBM_CLOUD_REGION: ${{ vars.IBM_CLOUD_REGION || 'ca-tor' }}
+  IBM_CLOUD_REGION: ${{ vars.IBM_CLOUD_REGION || 'us-south' }}
   CR_NAMESPACE: ${{ vars.IBM_CR_NAMESPACE || 'rag_modulo' }}
   # ICR uses shortened region names: us-south -> us, eu-gb -> uk, ca-tor -> ca, etc.
   ICR_REGION: ${{ vars.IBM_CLOUD_REGION == 'eu-gb' && 'uk' || (vars.IBM_CLOUD_REGION == 'us-south' && 'us' ||