feat(threads): thread panel header says who started it and when (#165)

The subtitle was only the room name. It now reads e.g. "Thread Lab · started
by alice, Fri 09:18 PM" (the user's clock/date preferences via the #139
formatter), which is what you want to know when arriving from the Threads
list. Verified in the 360 px desktop panel: fits without clipping.

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

src/app/features/room/thread/ThreadPanel.tsx

@@ -28,6 +28,8 @@ import {
   ThreadNotificationModeSwitcher,
 } from '../../../components/ThreadNotificationModeSwitcher';
 import { useThreadNotificationMode } from '../../../hooks/useThreadNotifications';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
+import { getMemberName } from '../../../utils/room';
 import { ThreadNotificationMode } from '../../../utils/threadNotifications';
 
 type ThreadPanelHeaderProps = {
@@ -37,6 +39,12 @@ type ThreadPanelHeaderProps = {
 };
 function ThreadPanelHeader({ room, threadId, requestClose }: ThreadPanelHeaderProps) {
   const mode = useThreadNotificationMode(room.roomId, threadId);
+  const { format } = useTimestampFormatter();
+  // [Gitea #165] Who started the thread and when — the first thing you want
+  // when arriving from the Threads list.
+  const root = room.findEventById(threadId) ?? room.getThread(threadId)?.rootEvent;
+  const rootSender = root?.getSender();
+  const startedBy = rootSender ? getMemberName(room, rootSender) : undefined;
 
   return (
     <Header className={css.ThreadPanelHeader} variant="Background" size="600">
@@ -47,6 +55,7 @@ function ThreadPanelHeader({ room, threadId, requestClose }: ThreadPanelHeaderPr
           </Text>
           <Text size="T200" truncate style={{ opacity: 0.65 }}>
             {room.name}
+            {startedBy && root && ` · started by ${startedBy}, ${format(root.getTs())}`}
           </Text>
         </Box>
         <Box shrink="No" alignItems="Center" gap="100">