ML-173: replace aws-sdk with aws4 + built-in fetch
Replace @aws-sdk/client-s3 (~150 transitive deps, ~14MB) with aws4
(0 transitive deps, ~40KB) and Node.js built-in fetch+crypto for
S3 ListObjectsV2 against Hetzner Object Storage.
- New s3-client.ts: SigV4 signing via aws4, regex-based XML parsing
with namespace tolerance, pagination support, 5 error categories
- 29 unit tests (node:test, zero-dependency) covering signing,
parsing, entities, missing fields, pagination, abort, errors
- Settlement guard for double done(null) on abort
- XML entity decoding and regex metacharacter escaping
- Dependency surface: 150 packages → 1 (aws4, single-file, auditable)
Claudio Ortolina
6f865a7b4d