fix: change cover background back to white to distinguish text areas from black mosaic gaps

Made-with: Cursor

src/cover.py

@@ -114,7 +114,7 @@ def generate_mosaic_cover(
 ) -> str:
     os.makedirs(output_dir, exist_ok=True)
     w, h = config.COVER_SIZE
-    img = PILImage.new("RGBA", (w, h), color=(0, 0, 0, 255))
+    img = PILImage.new("RGBA", (w, h), color=(245, 245, 245, 255))
 
     bottom_headlines_height = 0
     if headlines: