feat: configurable removalPolicy [INFRA-80168]

[ahammond]

Note

High Risk
High risk because it changes the default CloudFormation DeletionPolicy for core Aurora infrastructure from Retain to Delete, which can lead to accidental database/secret/security-group deletion on stack removal if consumers don’t explicitly set RemovalPolicy.RETAIN.

Overview
Makes removalPolicy functional again and changes the default behavior. AuroraProps.removalPolicy is no longer deprecated/ignored; it now drives an ApplyRemovalPolicyAspect that applies the chosen policy to infrastructure resources (RDS cluster/instances, KMS key, Secrets Manager secrets/attachments, security groups, parameter/subnet groups), while ephemeral resources (Lambda/IAM/nested stacks/log groups/etc.) remain forced to RemovalPolicy.DESTROY.

Breaking change: the default for infrastructure resources flips from automatic RETAIN to DESTROY (CloudFormation DeletionPolicy Delete/unset). Tests are updated to assert the new default and that explicitly setting RemovalPolicy.RETAIN retains infrastructure resources, and CLAUDE.md is updated to document the transition.

^{Written by Cursor Bugbot for commit 6f573ac. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.62%. Comparing base (1e8e664) to head (836943b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #142      +/-   ##
==========================================
- Coverage   96.63%   96.62%   -0.02%     
==========================================
  Files           6        6              
  Lines        1843     1837       -6     
  Branches      184      185       +1     
==========================================
- Hits         1781     1775       -6     
  Misses         62       62              

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