The quick-add parser rejected every IPv6 proxy: the host group [^:]+
cannot match IPv6 literals (colons) and the pattern had no bracketed
form, so lines like socks5://[2001:db8::1]:1080 were reported invalid.
Add a bracketed-IPv6 host alternative and strip the brackets before
storing; the backend re-brackets via net.JoinHostPort when building the
proxy URL. Bare (unbracketed) IPv6 stays rejected because it is
ambiguous with host:port. Also add a regression test.
lbyxiaolizi
ee62dfbaf1