fix(composer): recover silently from a composer render error; capture details

Reported on chat.lotusguild.org: picking a name from the @-mention list
showed "The message composer hit a snag." — clicking OK continued with the
draft intact. The composer's known failure mode is a transient render error
right after an autocomplete insert (slate-react's DOM selection sync racing
the model; 477df4ae fixed one such path). It did not reproduce locally in 60
attempts (click / Enter / Tab, fast and slow, display names with spaces and
emoji, Chromium and WebKit), so this makes it harmless and diagnosable:

- ComposerErrorBoundary: the first failure clears the selection and remounts
  the composer immediately, with no notice (the draft is intact). A second
  failure within 5 s shows the notice, now saying the draft is safe, with
  "Reload composer" and "Copy details" (time, error, stack, component stack,
  browser). Every failure is logged to the console as "[composer] render
  error".
- Used for the room composer and, newly, the thread panel composer (which had
  no boundary, so the same error took the whole panel down).

Verified with a temporary injected crash (not committed): one crash recovers
with the draft kept and no notice; two within 5 s show the notice, Copy
details copies the report, Reload composer restores the full draft.
Chromium e2e 19 passed.

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

@@ -23,6 +23,7 @@ import { useKeyDown } from '../../../hooks/useKeyDown';
 import { useSetting } from '../../../state/hooks/settings';
 import { settingsAtom } from '../../../state/settings';
 import { RoomInput } from '../RoomInput';
+import { ComposerErrorBoundary } from '../ComposerErrorBoundary';
 import {
   getThreadNotificationModeIcon,
   ThreadNotificationModeSwitcher,
@@ -204,15 +205,17 @@ export function ThreadPanel({ room, threadId, requestClose }: ThreadPanelProps)
             <ThreadTimeline room={room} thread={thread} editor={editor} />
           </Box>
           <Box className={css.ThreadPanelInput} shrink="No" direction="Column">
-            <RoomInput
-              room={room}
-              roomId={room.roomId}
-              threadRootId={threadId}
-              editor={editor}
-              editableName="ThreadInput"
-              fileDropContainerRef={fileDropContainerRef}
-              compactLayout
-            />
+            <ComposerErrorBoundary editor={editor}>
+              <RoomInput
+                room={room}
+                roomId={room.roomId}
+                threadRootId={threadId}
+                editor={editor}
+                editableName="ThreadInput"
+                fileDropContainerRef={fileDropContainerRef}
+                compactLayout
+              />
+            </ComposerErrorBoundary>
           </Box>
         </>
       )}