Pass top-level region through all Trail child resources and lookups

[corymhall]

Parent: #1933

awsx:cloudtrail:Trail exposes a top-level region input, but the implementation does not consistently thread that region through all child resources and region-sensitive operations.

Known child/defaulted paths to audit:

• required bucket creation
• bucket policy creation
• optional log group creation
• default role creation
• root aws.cloudtrail.Trail resource
• any account/identity lookups that need region-aware behavior

Implementation references:

• awsx/schema-types.ts (TrailArgs.region)
• awsx/cloudtrail/trail.ts
• awsx/s3/bucket.ts
• awsx/cloudwatch/logGroup.ts
• awsx/role.ts

Acceptance criteria:

• top-level region is passed to all Trail child AWS resources that support it
• region-aware invokes/lookups used by Trail receive the top-level region when present
• targeted tests cover the changed behavior