refactor(database): migrate to new modular database layer and unify data access

- Remove legacy database.ts, LocalDataSource.ts, and MessageRepository.ts
- Create new src/database/ module with messageRepository, userCacheRepository, conversationRepository, and groupCacheRepository
- Update all consumers to import from @/database instead of services/database
- Add web platform blur handling for modal components to fix focus issues
- Flatten SystemMessageItem and NotificationsScreen styles for consistent design
- Add draggable slider in ChatSettingsScreen and dynamic font size support
- Introduce 9 new chat color themes
- Add profile screens for about, terms, and privacy policy with navigation routes
- Add policy links to login and registration screens
- Fix post share URL format from /posts/ to /post/

src/screens/message/PrivateChatInfoScreen.tsx

@@ -21,10 +21,7 @@ import { useAuthStore } from '../../stores';
 import { authService } from '../../services/authService';
 import { messageService } from '../../services/messageService';
 import { ApiError } from '../../services/api';
-import {
-  clearConversationMessages,
-  getConversationCache,
-} from '../../services/database';
+import { messageRepository, conversationRepository } from '@/database';
 import { messageManager } from '../../stores/messageManager';
 import { userManager } from '../../stores/userManager';
 import { Avatar, Text, Button, Loading, Divider } from '../../components/common';
@@ -81,7 +78,7 @@ const PrivateChatInfoScreen: React.FC = () => {
         return;
       }
 
-      const cached = await getConversationCache(conversationId);
+      const cached = await conversationRepository.getCache(conversationId);
       if (cached) {
         setIsPinned(Boolean((cached as any).is_pinned));
         return;
@@ -137,7 +134,7 @@ const PrivateChatInfoScreen: React.FC = () => {
           style: 'destructive',
           onPress: async () => {
             try {
-              await clearConversationMessages(conversationId);
+              await messageRepository.clearConversation(conversationId);
               Alert.alert('成功', '聊天记录已清空');
             } catch (error) {
               Alert.alert('错误', '清空聊天记录失败');