Mail list: fall back to first names when the senders run long

Past 25 characters the joined sender column truncated mid-name. It now
shows each sender's first word instead ("Alice, me, Bob"), a bare address
by its local part, and the user's own accounts still as "me".

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

frontend/src/components/list/MessageList.tsx

@@ -33,6 +33,28 @@ function initials(p: Address | undefined): string {
   return name.slice(0, 2).toUpperCase();
 }
 
+// Past this many characters the sender column switches to first names only.
+const SENDERS_FULL_MAX = 25;
+
+// 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`.
+export function senderNames(
+  senders: Address[],
+  isMe: (a: Address) => boolean,
+  me: string,
+): string {
+  const full = senders.map((a) => (isMe(a) ? me : a.name || a.email)).join(", ");
+  if (full.length <= SENDERS_FULL_MAX) return full;
+  return senders
+    .map((a) => {
+      if (isMe(a)) return me;
+      const name = a.name.trim();
+      return name ? name.split(/\s+/)[0] : a.email.split("@")[0];
+    })
+    .join(", ");
+}
+
 // Monocolor paperclip (inherits currentColor) — replaces the old emoji.
 function Paperclip() {
   return (
@@ -137,9 +159,7 @@ export function MessageList({
           // with the user's own accounts shown as "me" — so a thread you started
           // and someone answered reads "me, Alice". Recipients are not listed.
           const senders = thread.senders.length ? thread.senders : thread.participants.slice(0, 1);
-          const names = senders.length
-            ? senders.map((a) => (isMe(a) ? t("mail.me") : a.name || a.email)).join(", ")
-            : "(no one)";
+          const names = senders.length ? senderNames(senders, isMe, t("mail.me")) : "(no one)";
           // The avatar is the other side of the conversation where there is one.
           const primary = senders.find((a) => !isMe(a)) ?? senders[0];
           // The badge still counts everyone involved — the name is narrowed, the