Remove custom SubscriptionManager class and adopt Zustand's built-in
selector mechanism for reactive state updates. This simplifies the
architecture by eliminating manual subscription management and relying
on Zustand's automatic dependency tracking for component re-renders.
Key changes:
- Remove SubscriptionManager class from store.ts
- Replace all notifySubscribers calls with direct store updates
- Update hooks to use Zustand selectors with useShallow for complex data
- Remove subscribe/unsubscribe patterns from MessageManager
- Simplify EmbeddedChat to use selector instead of local state
- Rename requestConversationListRefresh to refreshConversations
- Remove MessageStateManager wrapper layer in favor of direct zustand store
- Move service modules to services/ subdirectory (ConversationOperations, MessageDeduplication, MessageSendService, MessageSyncService, ReadReceiptManager, UserCacheService, WSMessageHandler)
- Add new zustand-based store with subscriptionManager for event handling
- Introduce React hooks for message state (useConversations, useMessages, useUnreadCount, etc.)
- Update exports in index.ts to reflect new module structure
- Deprecate messageManager.ts entry point in favor of message/index.ts
- Maintain backward compatibility with existing MessageManager API
