Mail list: cut a lone long sender name at 21 characters plus "..."

A single sender showed in full (or, past 25 characters, as a first word).
Past 22 characters it now shows the first 21 and "...". Several senders
keep the full-names / first-words presentation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/list/MessageList.tsx

@@ -35,15 +35,23 @@ function initials(p: Address | undefined): string {
 
 // Past this many characters the sender column switches to first names only.
 const SENDERS_FULL_MAX = 25;
+// A lone sender's name longer than this is cut to one character less plus "...".
+const SINGLE_SENDER_MAX = 22;
 
-// The sender column's text: full names joined, or — when that would run past
-// SENDERS_FULL_MAX — each sender's first word ("Alice Smith" -> "Alice", a bare
-// address -> its local part). The user's own accounts are always `me`.
+// The sender column's text. A single sender shows in full, or cut at
+// SINGLE_SENDER_MAX. Several show as full names joined, or — when that would run
+// past SENDERS_FULL_MAX — each sender's first word ("Alice Smith" -> "Alice", a
+// bare address -> its local part). The user's own accounts are always `me`.
 export function senderNames(
   senders: Address[],
   isMe: (a: Address) => boolean,
   me: string,
 ): string {
+  if (senders.length === 1) {
+    const [a] = senders;
+    const name = isMe(a) ? me : a.name || a.email;
+    return name.length > SINGLE_SENDER_MAX ? `${name.slice(0, SINGLE_SENDER_MAX - 1)}...` : name;
+  }
   const full = senders.map((a) => (isMe(a) ? me : a.name || a.email)).join(", ");
   if (full.length <= SENDERS_FULL_MAX) return full;
   return senders