refactor: Deduplicated BMP header writing in Xtc (#1439)

## Summary

**What is the goal of this PR?**

Replaced manual 1-bit BMP header logic in `Xtc::generateCoverBmp()` and
`Xtc::generateThumbBmp()` with calls to the existing `createBmpHeader()`
utility. Added a `BmpRowOrder` enum and param to support the top-down
row order of XTC cover images.

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src/util/ScreenshotUtil.cpp

@@ -62,7 +62,7 @@ bool ScreenshotUtil::saveFramebufferAsBmp(const char* filename, const uint8_t* f
 
   BmpHeader header;
 
-  createBmpHeader(&header, phyWidth, phyHeight);
+  createBmpHeader(&header, phyWidth, phyHeight, BmpRowOrder::BottomUp);
 
   bool write_error = false;
   if (file.write(reinterpret_cast<uint8_t*>(&header), sizeof(header)) != sizeof(header)) {