feat: personal room name overrides (MSC4431-style)

Users can right-click any room and 'Rename for me...' to set a local
display name visible only to them. Stored in account data under
io.lotus.room_names. Shows a pencil indicator on renamed rooms.
useLocalRoomName() hook overrides useRoomName() when a local name exists.

Also includes:
- Rich room topic rendering via RoomTopicContent object (formatted_body
  support in RoomTopicViewer with HTML sanitization via sanitizeCustomHtml)
- Edit history viewer: clicking '(edited)' on a message opens a modal
  showing all prior versions with timestamps (EditHistoryModal.tsx)

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

src/app/components/room-intro/RoomIntro.tsx

@@ -66,7 +66,7 @@ export const RoomIntro = as<'div', RoomIntroProps>(({ room, ...props }, ref) =>
             {name}
           </Text>
           <Text size="T400" priority="400">
-            {typeof topic === 'string' ? topic : 'This is the beginning of conversation.'}
+            {topic?.topic ?? 'This is the beginning of conversation.'}
           </Text>
           {creatorName && ts && (
             <Text size="T200" priority="300">