fix(presence): Do Not Disturb is real "busy" presence and keeps your status (#283)

DND was sent as presence unavailable with the literal status text
"dnd": it replaced your status, and other clients showed "dnd". Where
the server supports MSC3026 (busy_presence), DND now sends presence
org.matrix.msc3026.busy and leaves the status alone (Synapse keeps
busy across /sync set_presence=online). Busy renders as red "Do Not
Disturb" with the real status line; the legacy unavailable + "dnd"
encoding is still recognised and still used on servers without it.
Status saves / clears no longer downgrade busy. The SDK rejects
non-spec presences, so busy goes through a direct authed PUT.

Fixes #283

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/features/settings/account/Profile.tsx

@@ -38,7 +38,11 @@ import { SettingTile } from '../../../components/setting-tile';
 import { useMatrixClient } from '../../../hooks/useMatrixClient';
 import { getAccountData, setAccountData } from '../../../utils/accountData';
 import { presenceStateFromSetting } from '../../../hooks/usePresenceUpdater';
-import { describePresenceError, setPresenceWithRetry } from '../../../utils/presenceWrite';
+import {
+  describePresenceError,
+  setPresenceWithRetry,
+  writePresence,
+} from '../../../utils/presenceWrite';
 import { useSetting } from '../../../state/hooks/settings';
 import { settingsAtom } from '../../../state/settings';
 import { UserProfile, useUserProfile } from '../../../hooks/useUserProfile';
@@ -554,7 +558,7 @@ function ProfileStatus() {
     localStorage.removeItem(STATUS_MSG_KEY(userId));
     localStorage.removeItem(STATUS_EXPIRY_KEY(userId));
     // Preserve the user's chosen presence when clearing the status message.
-    mx.setPresence({
+    writePresence(mx, {
       presence: presenceStateFromSetting(presenceStatus, hidePresence),
       status_msg: '',
     }).catch(() => undefined);