fix(gen2-migration): refactor breaks when auth triggers are placed outside of the auth stack in gen2

[iliapolo]

Description of changes

Fixes a refactor failure when an auth trigger Lambda lives in a separate stack from the auth stack. When the trigger is co-located in the auth stack, the UserPool references it via Fn::GetAtt within the same stack — which our resolvers already handled. When the trigger is in a separate stack, CDK instead threads the Lambda ARN into the auth stack as a CloudFormation parameter. resolveTarget() was not running parameter resolution, so that {"Ref": "referencetoamplify...Arn"} survived into the holding stack template as a dangling reference, causing CloudFormation to reject it with "Unresolved resource dependencies."

The fix applies resolveParameters to the Gen2 target template before resolveDependencies, consistent with how resolveSource() already works. The reason we didn't see this before in fitness tracker (which has an auth trigger) is because we manually forced the trigger to placed in the auth stack (using resourceGroupName) to avoid circular dependency issues - but those issues were not actually caused by the auth trigger, so its not needed.

Core fix

resolveTarget() in ForwardCategoryRefactorer now runs resolveParameters before resolveDependencies, consistent with resolveSource().

Migration app cleanup

Removed the setResourceGroupName workaround for the pre-signup trigger from fitness-tracker/migration/post-generate.ts.

Snapshot regeneration

Snapshots updated to reflect the corrected template resolution output.

Issue #, if available

Fixes #14746

Description of how you validated changes

• Snapshots regenerated and reviewed to confirm cross-stack parameter
  references are resolved in the Gen2 target template before dependency
  stripping.
• The fitness-tracker migration app no longer requires the manual
  resource group workaround.

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

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