The songgao/water library's InterfaceName parameter is a selection filter
that searches the Windows registry for an existing adapter with a matching
friendly name — it cannot name a new adapter during creation. Passing
name=tap0 caused the library to fail before even creating the adapter.
Fix by omitting InterfaceName from water.New(), letting Windows auto-name
the adapter, then renaming via netsh if a custom name was specified.
Also add directory validation to file handler to catch misconfig early.
Add PUT method support to the file:// handler, allowing file uploads via
curl -T. Upload is opt-in, disabled by default — enable with ?put=true
metadata flag. Includes path traversal protection.
Fix bugs in the file handler: unbuffered send channel deadlock on Close,
conn leak when send drops on done, and Addr() returning nil. Add done-
priority select in send(), explicit ln.Close() in Close(), Unwrap() on
responseWriter for http.ResponseController, and nil guards.
Also add package doc, NewHandler doc, and 39 unit tests covering the
listener, responseWriter, handler lifecycle, auth, and file serving.
ginuerzh