fix: P0 post-deploy bug fixes from live testing

- EditHistoryModal: use raw fetch with /_matrix/client/v1/ path for
  relations API — Synapse only supports relations at v1, not v3 (fixes
  Sentry JAVASCRIPT-REACT-K / 404 error)
- RoomViewHeader: remove useReportRoomSupported spec-version gate —
  Synapse 1.114+ has the endpoint but only advertises spec v1.12;
  button now always shows for non-creator, non-server-notice rooms
- ReportRoomModal: handle M_UNRECOGNIZED/404 with "not supported by
  your homeserver" message
- RoomNavItem: add isServerNotice guard to Room Settings in sidebar
  context menu (was only guarded in header three-dots menu)
- initMatrix: bump setMaxListeners from 50 → 150 to prevent
  MaxListenersExceededWarning with large room lists
- RoomProfile: save topic with formatted_body + format when markdown
  syntax is detected; add markdown hint below topic textarea

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

src/app/features/common-settings/general/RoomProfile.tsx

@@ -41,6 +41,32 @@ import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
 import { useAlive } from '../../../hooks/useAlive';
 import { RoomPermissionsAPI } from '../../../hooks/useRoomPermissions';
 
+const MARKDOWN_PATTERN = /(\*\*|__|\*|_|~~|`|\[.+?\]\(.+?\))/;
+
+function topicMarkdownToHtml(text: string): string {
+  return text
+    .replace(/&/g, '&')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+    .replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>')
+    .replace(/__(.+?)__/g, '<strong>$1</strong>')
+    .replace(/\*(.+?)\*/g, '<em>$1</em>')
+    .replace(/_(.+?)_/g, '<em>$1</em>')
+    .replace(/~~(.+?)~~/g, '<del>$1</del>')
+    .replace(/`(.+?)`/g, '<code>$1</code>')
+    .replace(/\[(.+?)\]\((.+?)\)/g, '<a href="$2">$1</a>')
+    .replace(/\n/g, '<br>');
+}
+
+function buildTopicContent(topic: string): Record<string, string> {
+  if (!MARKDOWN_PATTERN.test(topic)) return { topic };
+  return {
+    topic,
+    format: 'org.matrix.custom.html',
+    formatted_body: topicMarkdownToHtml(topic),
+  };
+}
+
 type RoomProfileEditProps = {
   canEditAvatar: boolean;
   canEditName: boolean;
@@ -101,7 +127,8 @@ export function RoomProfileEdit({
           await mx.sendStateEvent(room.roomId, StateEvent.RoomName as any, { name: roomName });
         }
         if (roomTopic !== undefined) {
-          await mx.sendStateEvent(room.roomId, StateEvent.RoomTopic as any, { topic: roomTopic });
+          const topicContent = buildTopicContent(roomTopic);
+          await mx.sendStateEvent(room.roomId, StateEvent.RoomTopic as any, topicContent);
         }
       },
       [mx, room.roomId],
@@ -224,10 +251,16 @@ export function RoomProfileEdit({
         <TextArea
           name="topicTextArea"
           defaultValue={topic}
+          placeholder="Describe this room. Markdown supported: **bold**, *italic*, [link](url)"
           variant="Secondary"
           radii="300"
           readOnly={!canEditTopic || submitting}
         />
+        {canEditTopic && (
+          <Text size="T200" priority="300">
+            Supports markdown: **bold**, *italic*, ~~strikethrough~~, `code`, [text](url)
+          </Text>
+        )}
       </Box>
       {submitState.status === AsyncStatus.Error && (
         <Text size="T200" style={{ color: color.Critical.Main }}>