fix(workflow): Add SKIP_AUTH default value to prevent Pydantic validation errors

This PR fixes Pydantic validation errors that were occurring when the SKIP_AUTH secret was empty.

## Problem

When SKIP_AUTH secret is not set or empty, the backend receives an empty string '', causing:
```
Input should be a valid boolean, unable to interpret input
[type=bool_parsing, input_value='', input_type=str]
```

This was causing backend deployments to fail during the Code Engine application startup.

## Solution

Added default value 'false' to SKIP_AUTH environment variable:

**Before**:
```yaml
SKIP_AUTH: ${{ secrets.SKIP_AUTH }}
```

**After**:
```yaml
SKIP_AUTH: ${{ secrets.SKIP_AUTH || 'false' }}
```

Now when the secret is empty, the backend receives 'false' instead of '', which Pydantic can parse as a boolean.

## Testing

This fix will be validated in the next deployment workflow run. Expected behavior:
- If SKIP_AUTH secret is set: uses that value
- If SKIP_AUTH secret is empty/unset: defaults to 'false'
- Backend starts successfully without Pydantic validation errors

## Related

- Part of deployment fixes series (breaking down PR #641)
- Related to PR #642 (backend Docker fixes)

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

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

Author: manavgup

.github/workflows/deploy_complete_app.yml

@@ -85,7 +85,9 @@ env:
   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' || (vars.IBM_CLOUD_REGION == 'us-east' && 'us' || (vars.IBM_CLOUD_REGION == 'ca-tor' && 'ca' || vars.IBM_CLOUD_REGION))) }}
+  ICR_REGION: ${{ vars.IBM_CLOUD_REGION == 'eu-gb' && 'uk' || (vars.IBM_CLOUD_REGION == 'us-south' && 'us' ||
+    (vars.IBM_CLOUD_REGION == 'us-east' && 'us' || (vars.IBM_CLOUD_REGION == 'ca-tor' && 'ca' ||
+    vars.IBM_CLOUD_REGION))) }}
 
 # Prevent concurrent deployments to avoid conflicts
 concurrency:
@@ -341,7 +343,7 @@ jobs:
           APP_NAME: ${{ env.BACKEND_APP_NAME }}
           IBM_CLOUD_REGION: ${{ env.IBM_CLOUD_REGION }}
           IBM_CLOUD_RESOURCE_GROUP: ${{ vars.IBM_CLOUD_RESOURCE_GROUP || 'rag-modulo-deployment' }}
-          SKIP_AUTH: ${{ secrets.SKIP_AUTH }}
+          SKIP_AUTH: ${{ secrets.SKIP_AUTH || 'false' }}
           OIDC_DISCOVERY_ENDPOINT: ${{ secrets.OIDC_DISCOVERY_ENDPOINT }}
           IBM_CLIENT_ID: ${{ secrets.IBM_CLIENT_ID }}
           IBM_CLIENT_SECRET: ${{ secrets.IBM_CLIENT_SECRET }}