fix(composer): only offer a token row the opener can honor

The right-click token action offered "Open link" for any `scheme://…` run,
including the ones `useOpenLinkOrFile` refuses (`ftp://`, `vscode://`,
`slack://`, `javascript://`): a row whose only outcome was the opener's
unsupported-protocol toast. Ask the opener first — `canOpenLinkOrFile` is
the same pair of checks it branches on. A path is still asked the narrower
question, so a protocol-relative `//cdn.example.com/x` (classified as a
path, opened as https) cannot appear under an "Open file" label.

A right click inside a hand-made selection read that selection with a bare
`textBetween`, which drops reference badges and hard breaks: selecting
`https://example.com` ⏎ `/private` glued into one token and offered to open
a url that is nowhere in the document. Both separators are now a newline,
so any non-text node disqualifies the run.