Fix: Enable baseDnsZone support for single-image stacks (AWS Lambda)

[universe-ops]

Problem

The baseDnsZone configuration was working correctly for cloud-compose stacks (ECS Fargate) but not for single-image stacks (AWS Lambda). While the field was defined in StackConfigSingleImage, the AWS Lambda implementation wasn't properly exposing it through the required OverriddenBaseZone() interface method.

Root Cause

• EcsFargateInput had a BaseDnsZone field and implemented OverriddenBaseZone() method ✅
• LambdaInput was missing the OverriddenBaseZone() method ❌
• This prevented DNS zone override functionality from working with AWS Lambda deployments

Solution

Added the missing OverriddenBaseZone() method to LambdaInput that returns l.StackConfig.BaseDnsZone directly, eliminating the need for field duplication.

Changes

• Added: OverriddenBaseZone() method to LambdaInput struct in pkg/clouds/aws/aws_lambda.go
• Implementation: Returns l.StackConfig.BaseDnsZone directly (clean, no field duplication)

Impact

• ✅ baseDnsZone configuration now works for single-image stacks (AWS Lambda)
• ✅ Feature parity between cloud-compose and single-image deployment types
• ✅ Clean implementation without unnecessary field duplication

Usage Example

# client.yaml - Now works for single-image stacks!
stacks:
  my-lambda:
    type: single-image
    config:
      baseDnsZone: "my-custom-zone.com"
      domain: "api.my-custom-zone.com"
      # ... other config

Testing

• Code compiles successfully
• Follows existing patterns from ECS Fargate implementation
• No breaking changes to existing functionality