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/message/RemindMeDialog.tsx

@@ -1,8 +1,9 @@
-import React, { useMemo } from 'react';
+import React, { useMemo, useState } from 'react';
 import FocusTrap from 'focus-trap-react';
 import {
   Box,
   Button,
+  color,
   config,
   Dialog,
   Header,
@@ -43,15 +44,25 @@ export function RemindMeDialog({ roomId, eventId, previewText, onClose }: Remind
   const modalStyle = useModalStyle(320);
   const { addReminder } = useReminders();
   const presets = useMemo(() => getPresets(), []);
+  const [busy, setBusy] = useState(false);
+  const [error, setError] = useState<string | null>(null);
 
   const handlePick = async (ms: number) => {
-    await addReminder({
-      roomId,
-      eventId,
-      timestamp: Date.now() + ms,
-      message: previewText || 'Reminder',
-    });
-    onClose();
+    if (busy) return;
+    setBusy(true);
+    setError(null);
+    try {
+      await addReminder({
+        roomId,
+        eventId,
+        timestamp: Date.now() + ms,
+        message: previewText || 'Reminder',
+      });
+      onClose();
+    } catch {
+      setBusy(false);
+      setError('Could not set reminder. Try again.');
+    }
   };
 
   return (
@@ -108,6 +119,7 @@ export function RemindMeDialog({ roomId, eventId, previewText, onClose }: Remind
                   variant="Secondary"
                   fill="Soft"
                   radii="300"
+                  disabled={busy}
                   onClick={() => handlePick(p.ms)}
                 >
                   <Text size="B300" truncate>
@@ -115,6 +127,14 @@ export function RemindMeDialog({ roomId, eventId, previewText, onClose }: Remind
                   </Text>
                 </Button>
               ))}
+              {error && (
+                <Text
+                  size="T200"
+                  style={{ color: color.Critical.Main, paddingTop: config.space.S100 }}
+                >
+                  {error}
+                </Text>
+              )}
             </Box>
           </Dialog>
         </FocusTrap>