refactor: streamline post sync, fix image gallery, and clean up chat screen

- **Post sync optimization**: Clear store immediately when params change to prevent flashing old posts; replace instead of merge on refresh
- **ImageGallery fix**: Use idempotent download option, migrate to Asset.create() API, fix Android file path requirement, ensure proper cleanup
- **UserProfileScreen**: Add ImageGallery for post image viewing with consistent implementation
- **SearchScreen**: Add entrance animation and empty state
- **ChatScreen**: Remove unused state variables (lastSeq, firstSeq, isProgrammaticScrollRef) and dead imports

app.config.js

@@ -17,7 +17,7 @@ function getCommitCount() {
 // 在 commit count 上加偏移，保证 versionCode / buildNumber / runtimeVersion
 // 始终大于历史最大值（之前的最后一个版本是 5547），避免被系统/Play Store
 // 误判为降级。后续即使 commit count 重置或换仓库，偏移也能保证单调递增。
-const BUILD_NUMBER_OFFSET = 10000;
+const BUILD_NUMBER_OFFSET = 100000;
 
 const commitCount = getCommitCount();
 const buildNumber = String(parseInt(commitCount, 10) + BUILD_NUMBER_OFFSET);