feat: presence fix, voice ringing fix, user private notes + doc updates

- usePresenceUpdater: replace stale closure with readStatus() called at
  invocation time so changing custom status in Profile Settings is never
  silently overwritten by subsequent activity events
- CallEmbedProvider: fix m.space.parent state-key lookup by switching
  getStateEvent → getStateEvents (plural); space channel voice rooms no
  longer trigger the incoming-call ring/animation
- Add useUserNotes hook (io.lotus.user_notes account data, reactive via
  useAccountDataCallback, 500-char limit, cross-device sync)
- UserRoomProfile: add UserPrivateNotes textarea with 800ms debounced
  auto-save, saving indicator, char counter when <100 chars remain;
  shown only when viewing another user's profile
- LOTUS_FEATURES.md: add Private Notes section, Status Revert fix note,
  animation improvements subsection, Seasonal Themes section
- LOTUS_BUGS.md: mark presence revert + voice ringing bugs as resolved
- README.md + landing/index.html: document all new June 2026 features

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

src/app/hooks/useUserNotes.ts

@@ -0,0 +1,56 @@
+import { useCallback, useEffect, useState } from 'react';
+import { MatrixClient } from 'matrix-js-sdk';
+import { useMatrixClient } from './useMatrixClient';
+import { useAccountDataCallback } from './useAccountDataCallback';
+
+const NOTES_KEY = 'io.lotus.user_notes';
+export const USER_NOTE_MAX_LENGTH = 500;
+
+type UserNotesContent = Record<string, string>;
+
+function readNotes(mx: MatrixClient): UserNotesContent {
+  return (mx.getAccountData(NOTES_KEY as any)?.getContent() as UserNotesContent | undefined) ?? {};
+}
+
+export function useUserNotes(): {
+  getNote: (userId: string) => string;
+  setNote: (userId: string, note: string) => Promise<void>;
+} {
+  const mx = useMatrixClient();
+  const [notes, setNotes] = useState<UserNotesContent>(() => readNotes(mx));
+
+  useAccountDataCallback(
+    mx,
+    useCallback(
+      (evt) => {
+        if (evt.getType() === NOTES_KEY) {
+          setNotes(evt.getContent<UserNotesContent>() ?? {});
+        }
+      },
+      [],
+    ),
+  );
+
+  useEffect(() => {
+    setNotes(readNotes(mx));
+  }, [mx]);
+
+  const getNote = useCallback((userId: string) => notes[userId] ?? '', [notes]);
+
+  const setNote = useCallback(
+    async (userId: string, note: string) => {
+      const current = readNotes(mx);
+      const updated = { ...current };
+      const trimmed = note.trim().slice(0, USER_NOTE_MAX_LENGTH);
+      if (trimmed) {
+        updated[userId] = trimmed;
+      } else {
+        delete updated[userId];
+      }
+      await (mx as any).setAccountData(NOTES_KEY, updated);
+    },
+    [mx],
+  );
+
+  return { getNote, setNote };
+}