fix(PostImages, CreatePostScreen): adjust image gap for improved layout consistency

- Reduced image gap in PostImages and CreatePostScreen components from 12 to 4 (desktop) and 8 to 2 (mobile) for better spacing.
- Updated ImageGrid component to modify grid item widths for enhanced layout.
- Refactored PostRepository to improve local caching logic, ensuring non-blocking UI updates during cache writes.
- Introduced saveConversationsWithRelatedCache function to streamline conversation, user, and group data saving in the database.

src/screens/create/CreatePostScreen.tsx

@@ -128,11 +128,11 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
 
   // 响应式图片网格配置
   const imagesPerRow = useResponsiveValue({ xs: 3, sm: 3, md: 4, lg: 5, xl: 6 });
-  const imageGap = 8;
+  const imageGap = 4;
   const availableWidth = isWideScreen 
     ? Math.min(width, 800) - spacing.lg * 2 
     : width - spacing.lg * 2;
-  const imageSize = (availableWidth - imageGap * (imagesPerRow - 1)) / imagesPerRow;
+  const imageSize = Math.floor((availableWidth - imageGap * (imagesPerRow - 1)) / imagesPerRow);
   const contentInputMinHeight = Math.max(
     isWideScreen ? 460 : 320,
     Math.floor(windowHeight * (isWideScreen ? 0.56 : 0.5))
@@ -896,7 +896,7 @@ function createCreatePostStyles(colors: AppColors) {
     flexWrap: 'wrap',
     paddingHorizontal: 0,
     paddingTop: spacing.md,
-    gap: 8,
+    gap: 4,
   },
   imageGridItem: {
     borderRadius: borderRadius.md,