feat(performance): migrate FlatList to FlashList and add animations

Replace FlatList with FlashList across all message screens (ChatScreen, MessageListScreen, NotificationsScreen, HomeScreen) for improved list virtualization performance. Use `drawDistance={250}` instead of manual pagination. Simplify React.memo comparisons in MessageBubble and SegmentRenderer by removing function prop checks to prevent unnecessary re-renders.

Add AsyncStorage persistence for lastSystemMessageAt to avoid showing current time on first render. Include enter animations (fade and slide) for CreateGroupScreen and modernize UI styling to flat design.

BREAKING CHANGE: Upgrade @shopify/flash-list from 2.0.2 to ^2.3.1

src/stores/message/store.ts

@@ -9,11 +9,14 @@
  */
 
 import { create } from 'zustand';
+import AsyncStorage from '@react-native-async-storage/async-storage';
 import type {
   ConversationResponse,
   MessageResponse,
 } from '../../types/dto';
 
+const LAST_SYSTEM_MESSAGE_AT_KEY = 'last_system_message_at';
+
 // ==================== 状态接口 ====================
 
 /**
@@ -322,6 +325,11 @@ export const useMessageStore = create<MessageStore>((set, get) => ({
 
   setLastSystemMessageAt: (time: string | null) => {
     set({ lastSystemMessageAt: time });
+    if (time) {
+      AsyncStorage.setItem(LAST_SYSTEM_MESSAGE_AT_KEY, time).catch(() => {});
+    } else {
+      AsyncStorage.removeItem(LAST_SYSTEM_MESSAGE_AT_KEY).catch(() => {});
+    }
   },
 
   setSSEConnected: (connected: boolean) => {
@@ -380,6 +388,14 @@ export const useMessageStore = create<MessageStore>((set, get) => ({
       typingUsersMap: new Map(),
       mutedStatusMap: new Map(),
     });
+    AsyncStorage.removeItem(LAST_SYSTEM_MESSAGE_AT_KEY).catch(() => {});
   },
 }));
 
+export async function loadPersistedLastSystemMessageAt(): Promise<void> {
+  const time = await AsyncStorage.getItem(LAST_SYSTEM_MESSAGE_AT_KEY);
+  if (time) {
+    useMessageStore.setState({ lastSystemMessageAt: time });
+  }
+}
+