feat: presence avatar border rings (P5-18) + room emoji prefix support (P5-6)

P5-18: PresenceRingAvatar wrapper component applies a 2px box-shadow
ring to user avatars — green (online), yellow (idle/unavailable), red
(DND via status_msg='dnd'), no ring (offline). Applied to: message
timeline sender avatars, members drawer (members + knock requests),
@mention autocomplete, and inbox notification senders.

P5-6: Leading emoji in room names renders at 1.15× in the sidebar via
Unicode emoji regex detection in RoomNavItem. Emoji picker (EmojiBoard
in PopOut) added to all three room-name inputs: Create Room dialog
(converted to controlled input), Room Settings name field (shown only
when canEditName), and the "Rename for me" local rename dialog.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/components/presence/PresenceRingAvatar.tsx

@@ -0,0 +1,36 @@
+import React, { ReactNode } from 'react';
+import { color } from 'folds';
+import { Presence, useUserPresence } from '../../hooks/useUserPresence';
+
+function presenceRingColor(presence: Presence | undefined, status?: string): string | null {
+  if (!presence || presence === Presence.Offline) return null;
+  if (presence === Presence.Unavailable) {
+    return status === 'dnd' ? color.Critical.Main : color.Warning.Main;
+  }
+  return color.Success.Main;
+}
+
+type PresenceRingAvatarProps = {
+  userId: string;
+  children: ReactNode;
+};
+
+export function PresenceRingAvatar({ userId, children }: PresenceRingAvatarProps) {
+  const presence = useUserPresence(userId);
+  const ringColor = presenceRingColor(presence?.presence, presence?.status);
+
+  if (!ringColor) return <>{children}</>;
+
+  return (
+    <div
+      style={{
+        display: 'inline-flex',
+        borderRadius: '50%',
+        boxShadow: `0 0 0 2px ${ringColor}`,
+        flexShrink: 0,
+      }}
+    >
+      {children}
+    </div>
+  );
+}

src/app/components/presence/index.ts

@@ -1 +1,2 @@
 export * from './Presence';
+export * from './PresenceRingAvatar';