feat(harmony_assets): S3 credentials, folder upload, 19 tests
Fix S3Store to actually wire access_key_id/secret_access_key from config
into the AWS SDK credential provider. Add force_path_style for custom
endpoints (Ceph, MinIO). Add store_folder() for recursive directory upload.
New CLI command: upload-folder with --public-read/private ACL, env var
fallback for credentials, content-type auto-detection, progress bar.
Fix single-file upload --public-read default (was always true, now false).
Add 19 tests: Asset path computation, LocalStore fetch/cache/404/checksum
with httptest mocks, S3 key extraction, URL generation for custom/AWS
endpoints.
Jean-Gabriel Gill-Couture
c24fa9315b