fix: correct book card highlight padding by increasing tile height

Instead of shrinking the highlight strip (which clipped author text),
increase homeCoverTileHeight from 310 to 318 for proper bottom padding.
Revert double-padding subtraction in bottomH/bottomSectionHeight.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/GfxRenderer/GfxRenderer.cpp

@@ -279,7 +279,7 @@ void GfxRenderer::drawPixelDither<Color::LightGray>(const int x, const int y) co
 
 template <>
 void GfxRenderer::drawPixelDither<Color::DarkGray>(const int x, const int y) const {
-  drawPixel(x, y, (x + y) % 2 == 0);  // TODO: maybe find a better pattern?
+  drawPixel(x, y, (x + y) % 2 == 0);
 }
 
 void GfxRenderer::fillRectDither(const int x, const int y, const int width, const int height, Color color) const {