feat(message): support group avatar in navigation and chat screen

Pass group avatar through notification extras, navigation hrefs, and
route parameters. Update ChatScreen to resolve group information
(ID, name, and avatar) by prioritizing route parameters (e.g., from
push notifications) and falling back to conversation data from the
MessageManager.

- Update `NotificationBootstrap` to include `groupAvatar` in query params
- Update `hrefChat` to support `groupAvatar`
- Refactor `useChatScreen` to use `effectiveGroupId`, `effectiveGroupName`,
  and `effectiveGroupAvatar`
- Ensure `MessageManager` fetches conversation details if missing when
  activating a conversation
- Update `MessageListScreen` to pass `groupAvatar` during navigation

app/_layout.tsx

@@ -161,6 +161,7 @@ function NotificationBootstrap() {
           const conversationType = extras.conversation_type || extras.conversationType;
           const groupId = extras.group_id || extras.groupId;
           const groupName = extras.group_name || extras.groupName;
+          const groupAvatar = extras.group_avatar || extras.groupAvatar;
 
           if (conversationId) {
             const isGroup = conversationType === 'group';
@@ -169,6 +170,7 @@ function NotificationBootstrap() {
               q.set('isGroupChat', '1');
               if (groupId) q.set('groupId', groupId);
               if (groupName) q.set('groupName', groupName);
+              if (groupAvatar) q.set('groupAvatar', groupAvatar);
             } else if (senderId) {
               q.set('userId', senderId);
             }