Breaking change: S3Client.upload_from_bytes / upload_from_file now raise
on upload failure instead of returning {"action": "failed", ...}. Migration
guide in README and CHANGELOG.

- AioConfig.retries set to {max_attempts=1, mode=standard}; tenacity owns
  retries solely (no more 3x stacked attempts).
- list_objects passes PageSize=min(max_keys, 1000) to the paginator —
  small max_keys no longer pulls a full 1000-object first page.
- __aenter__ stores the aiobotocore client context manager and unwinds
  via the same CM in __aexit__ (removes latent fragility on close).
- Renamed _generate_url_from_file_with_result → _attach_presigned_url
  (used by both upload methods); typed dict[str, Any].
- Trimmed dead commented-out control-character check in _validate_s3_key;
  tightened its docstring.
- FileNamingStrategy docstring documents prefix="" → "file" fallback.

Tooling and infra:
- New CHANGELOG.md (Keep a Changelog, full history reconstructed back
  to 0.1.0).
- New .gitlab-ci.yml: lint (black --check, mypy) + pytest with cobertura
  coverage report.
- pyproject: [tool.mypy], [tool.black]; added types-aiofiles dev dep;
  bumped to 3.0.0.
- .gitignore rewritten in structured sections; added .ruff_cache, .vscode,
  Thumbs.db, secret patterns (*.pem, *.key, id_rsa*, credentials*,
  *.kubeconfig), coverage.xml.

Tests: 142 passing, 100% coverage. Updated upload-error tests for new
raise-based contract; added PaginationConfig PageSize coverage; rewired
async CM tests around the stored context manager.