D2-A: the library row's Share button becomes a single action — quickShareLink()
ensures a public link (minting on demand), copies it to the clipboard, and toasts
with an "Open in new tab" action. A copy failure still toasts (warning) with that
action so the link is never a dead end. Advanced controls (password/expiry/revoke/
user-ACL) stay in the existing ShareDialog, reached via a new "Manage sharing" row
button.
D1 (forward-only): CreateLinkIn.allow_download defaults to true, so a newly minted
link is downloadable by default. The default lives in the API, not a migration —
the download_links column default stays false, so no existing link flips. The
ShareDialog create-default is flipped to match.
Tests: TestCreateLinkDefault (default true; explicit false honored); 4 vitest cases
for quickShareLink (mint-vs-reuse, copy ok/fail, create failure). HU/EN parity.