feat(nav): draft indicator on room-nav items

Composer drafts persist per room, but nothing in the room list showed
which OTHER rooms had an unsent draft. Add a subtle chat-bubble icon on a
room's nav item when it has a message draft (and isn't the open room), so
half-written messages elsewhere are visible at a glance.

- Shared pure helper hasMsgDraft (utils/draft.ts, unit-tested) replaces
  the inline emptiness check; the composer DraftIndicator now reuses it.
- RoomNavItem reads a memoized selectAtom(draftAtom, hasMsgDraft) so a row
  re-renders only when its draft flag flips (the draft atom is written on
  room-leave, not per keystroke). Uses Icons.Message (pencil is reserved
  for the custom-name marker), muted, aria-label "Unsent draft".
- useHydrateMsgDrafts (mounted in ClientNonUIFeatures) pre-fills the
  per-room draft atoms from draft-msg-* localStorage on startup, so
  indicators are correct after a page reload, not only after revisiting a
  room. Thread drafts (key contains ::) are skipped; room-level only.

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

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -25,11 +25,8 @@ import { NOTIFICATION_SOUND_MAP } from '../../utils/notificationSounds';
 import { useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
 import { allInvitesAtom } from '../../state/room-list/inviteList';
-
-// Grace period after the initial sync settles before invite notifications arm, so
-// the async invite-atom population lands first and isn't mistaken for new invites.
-const INVITE_NOTIFY_ARM_DELAY_MS = 3000;
 import { useMatrixClient } from '../../hooks/useMatrixClient';
+import { useHydrateMsgDrafts } from '../../hooks/useHydrateMsgDrafts';
 import { getDirectRoomPath, getHomeRoomPath, getInboxInvitesPath } from '../pathUtils';
 import { mDirectAtom } from '../../state/mDirectList';
 import {
@@ -67,6 +64,10 @@ import {
   THREAD_NOTIFICATIONS_FALLBACK_BEHAVIOR,
 } from '../../utils/threadNotifications';
 
+// Grace period after the initial sync settles before invite notifications arm, so
+// the async invite-atom population lands first and isn't mistaken for new invites.
+const INVITE_NOTIFY_ARM_DELAY_MS = 3000;
+
 function isInQuietHours(start: string, end: string): boolean {
   const now = new Date();
   const [sh, sm] = start.split(':').map(Number);
@@ -865,9 +866,15 @@ function KeyboardShortcutsFeature() {
   return <KeyboardShortcutsDialog />;
 }
 
+function MsgDraftHydrator(): null {
+  useHydrateMsgDrafts();
+  return null;
+}
+
 export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
   return (
     <>
+      <MsgDraftHydrator />
       <SystemEmojiFeature />
       <PageZoomFeature />
       <FaviconUpdater />