composebox_typeahead: Move wildcard string to secondary in @-mention.

Earlier, in typeahead suggestions for wildcard mention, we rendered
wildcard string as primary text inside parentheses.

This commit separates the wildcard string as secondary_text to
be rendered without parentheses using styles like channel description.

Fixes: zulip#31245.

web/src/people.ts

@@ -33,6 +33,7 @@ export type SenderInfo = User & {
 export type PseudoMentionUser = {
     special_item_text: string;
     email: string;
+    secondary_text: string;
     pm_recipient_count: number;
     full_name: string;
     idx: number;