name quote-only drafts as such in the summary

a draft may contain only a quote,
without any text set yet.

these drafts cannot be sent, however, appear in the summary -
currently with the summary-text "", which results to sth.
as "Draft: " - which looks like an error or at least a bit weird.

this pr sets the summary text to "Reply" - similar to "Image", "Video" etc. -
the UI just expects some text here, not an empty string.

the result are summaries as "Draft: Reply" on all UIs -
which, btw. is also roughly the same what Signal does in this case.

src/stock.rs

@@ -240,6 +240,10 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "Chat protection disabled."))]
     ProtectionDisabled = 89,
+
+    // used in summaries, a noun, not a verb (not: "to reply")
+    #[strum(props(fallback = "Reply"))]
+    ReplyNoun = 90,
 }
 
 /*