fix(audit): correctness wave — ghost sends, Escape coordination, panel exclusion

- ScheduledMessagesTray: cancel prunes local state ONLY on confirmed server
  cancel; failures keep the item + show an inline error (was: a failed cancel
  looked cancelled but still sent at the scheduled time).
- Escape semantics: the composer consumes Escape (preventDefault+stopPropagation)
  iff autocomplete is open or a reply draft is set; the thread panel and Room's
  markAsRead act only on unconsumed Escape, and markAsRead defers entirely while
  a thread panel is open (listener order made it fire before the panel closed).
- Room: thread panel / media gallery are mutually exclusive (most-recently-
  opened wins); on mobile at most one right panel renders (thread > gallery >
  members) instead of stacked fullscreen overlays.
- RemindMeDialog: busy-disabled presets (no more double-click duplicates),
  try/catch with inline error, close only on success.
- ThreadTimeline: "Jump to Latest" floating chip when scrolled up (RoomTimeline
  idiom).

From the 4-auditor deep-audit wave; reviewer-verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/thread/ThreadTimeline.css.ts

@@ -11,6 +11,15 @@ export const ThreadTimelineContent = style({
   padding: `${config.space.S400} 0`,
 });
 
+export const ThreadTimelineFloat = style({
+  position: 'absolute',
+  bottom: config.space.S400,
+  left: '50%',
+  transform: 'translateX(-50%)',
+  zIndex: 1,
+  minWidth: 'max-content',
+});
+
 export const ThreadCentered = style({
   height: '100%',
   padding: config.space.S700,