fix(composer): a fully typed user ID + Enter sends as typed

d2503332 made Enter pick the mention suggestion, which also caught
"/kick @alice:server" + Enter (the e2e "/kick failure is reported" test):
typing a complete ID opens the mention list too, and Enter picked it instead
of running the command. Enter now picks only while a partial name is being
typed (no ':' in the query); a complete @user:server or #alias:server sends
as typed, like before.

Chromium e2e 19 passed; "@bo" + Enter still picks, ":smi" + Enter still
sends.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/editor/autocomplete/RoomMentionAutocomplete.tsx

@@ -140,7 +140,8 @@ export function RoomMentionAutocomplete({
   };
 
   useKeyDown(window, (evt: KeyboardEvent) => onTabPress(evt, pickTop));
-  useAutocompleteEnter(true, pickTop);
+  // Same rule as people: a fully typed #alias:server sends as typed.
+  useAutocompleteEnter(!query.text.includes(':'), pickTop);
 
   return (
     <AutocompleteMenu headerContent={<Text size="L400">Rooms</Text>} requestClose={requestClose}>

src/app/components/editor/autocomplete/UserMentionAutocomplete.tsx

@@ -140,9 +140,9 @@ export function UserMentionAutocomplete({
   };
 
   useKeyDown(window, (evt: KeyboardEvent) => onTabPress(evt, pickTop));
-  // The list always shows a suggestion (a member, or the typed id), so Enter
-  // always picks rather than sending "hey @bo".
-  useAutocompleteEnter(true, pickTop);
+  // Enter picks while a partial name is being typed ("hey @bo"). Once a full
+  // user ID has been typed ("/kick @alice:server"), Enter sends as typed.
+  useAutocompleteEnter(!query.text.includes(':'), pickTop);
 
   const getName = (member: RoomMember) => getMemberName(room, member.userId);