chore: update PgBouncer AMI pin (currently 20260218, 133 days old)

The PgBouncer EC2 AMI is pinned to `20260218`, which is 133 days old.

To find a more recent date-versioned path in your region:
```
aws ssm get-parameters-by-path \
--path "/aws/service/canonical/ubuntu/server/noble/stable/" \
--recursive \
--query "Parameters[?ends_with(Name, 'amd64/hvm/ebs-gp3/ami-id')].Name"
```

Then update the `DEFAULT_AMI_SSM_PARAMETER` constant in `lib/database/PgBouncer.ts`
and the `@default` tag in both `PgBouncer.ts` and `lib/database/index.ts`.

See: https://documentation.ubuntu.com/aws/aws-how-to/instances/find-ubuntu-images/

Run the provided AWS SSM query in the target region to find a newer date-versioned Ubuntu AMI path. Update DEFAULT_AMI_SSM_PARAMETER in lib/database/PgBouncer.ts and the @default tags in PgBouncer.ts and lib/database/index.ts. Done means all three references use the same current AMI version.

Written by the indexing model from the issue text.