folder-transfer v0.12.0

Added

• Parallel streams (-Streams <n>, default 4). Transfers now use several TCP connections at
  once, which lifts the single‑connection window ÷ RTT throughput ceiling — a large speed‑up on
  high‑latency links. The sender queues the shared folders and each connection pulls a whole folder
  at a time (runspace per connection on both sides), so the streams self‑balance. Small‑file
  bundling and adaptive compression still apply within each stream. Set -Streams 1 (or
  "streams": 1) for the classic single‑stream behavior; -Cutover forces single‑stream.

Notes / limitations

• Balance is per shared folder — a single giant folder is handled by one connection and is not
  split across streams. List its subfolders as separate folders entries to parallelize one big
  tree.
• In parallel mode, a whole top‑level folder deleted on the source is not auto‑removed on the
  receiver (files removed inside a folder still are). This keeps the per‑folder mirror simple and
  always correct; run once with -Streams 1 to prune vanished folders, or delete them by hand. The
  server and client print this caveat at startup when -Streams > 1.