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/components/business/PostCard/components/PostImages.tsx

@@ -16,7 +16,7 @@ const PostImages: React.FC<PostImagesProps> = ({ images, displayMode, onImagePre
   if (!images || images.length === 0) return null;
 
   // 计算图片间距和圆角
-  const imageGap = isDesktop ? 12 : 8;
+  const imageGap = isDesktop ? 4 : 2;
   const imageBorderRadius = isDesktop ? borderRadius.xl : borderRadius.md;
 
   return (

src/components/common/ImageGrid.tsx

@@ -132,10 +132,10 @@ function createImageGridStyles(colors: AppColors) {
       aspectRatio: 1,
     },
     gridItem2: {
-      width: '48%',
+      width: '49%',
     },
     gridItem3: {
-      width: '31%',
+      width: '32.5%',
     },
     masonryContainer: {
       flexDirection: 'row',