Fix S3 directory transfers and sync safety

[jhd3197]

Problem and behavior

S3 directory markers were treated as files during downloads, producing object head errors. Preserve exact S3 keys and folder markers across listing, copy, rename, deletion, search, and disk scans; sync now retains empty folders. Unicode, spaces, and percent characters remain intact.

Abort sync planning on incomplete source scans and defer mirror deletions until copies finish successfully. CLI copy honors explicit destination filenames, stages downloads before replacement, aborts failed multipart uploads, and returns failures for incomplete hashes and failed deletions.

Fixes #33.

Validation

• Local Moto audit: 55/55 CLI checks, including pagination and injected listing, download, upload, and hashing failures.
• Windows: 246 library tests and 7 CLI tests passed. One existing SSH-key ACL test was excluded on Windows; CI runs the unfiltered library suite on Linux.
• Three live S3 emulator transfer tests passed, including directory markers, Unicode bytes, and 200 MiB multipart/ranged transfer with a changed-source resume.
• TypeScript and CLI build passed.
• Enable CI for dev and run Rust tests plus the S3 CLI audit on PRs. See docs/s3-testing.md for reproducible setup and limits.

Wasabi itself has not been tested. Recursive and remote-to-remote CLI cp remain unsupported; use sync for directory transfers.