Ask before opening a shared item in a message

The share address takes a plain form POST, which any website can make,
and the app opened whatever arrived straight into a composer. It now
shows what was shared -- the title, the start of the text and link, and
the file names -- and opens a message only when the reader chooses to.
Discarding drops it.

Confirm dialogs now put a message that is not plain text in a div, since
the summary has blocks of its own.

Three new strings, translated in all nine catalogs.

web/src/ui/dialog.tsx

@@ -185,7 +185,8 @@ export function ConfirmHost() {
         )
       }
     >
-      {req.message && <p style={{ marginTop: 0 }}>{req.message}</p>}
+      {/* A paragraph for text; a block for anything with blocks of its own in it. */}
+      {req.message && (typeof req.message === "string" ? <p style={{ marginTop: 0 }}>{req.message}</p> : <div style={{ marginTop: 0 }}>{req.message}</div>)}
       {req.kind === "choice" && (
         <div className="dialog-choices">
           {req.choices?.map((c) => (