feat(home): Improve Continue Reading cover with 1-bit Atkinson dithering

- Add 1-bit BMP generation with Atkinson dithering for better quality thumbnails
- Replace noise dithering with error diffusion for smoother gradients
- Add fillPolygon() to GfxRenderer for proper bookmark ribbon shape
- Change bookmark from rect+triangle carve to pentagon polygon
- Fix bookmark inversion when Continue Reading card is selected
- Show selection state on first render (not just after navigation)
- Fix 1-bit BMP palette lookup in Bitmap::readRow()
- Add drawBitmap1Bit() optimized path for 1-bit BMPs
The 1-bit format eliminates gray passes on home screen for faster rendering
while Atkinson dithering maintains good image quality through error diffusion.

lib/GfxRenderer/Bitmap.cpp

@@ -341,7 +341,10 @@ BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer, int rowY) cons
     }
     case 1: {
       for (int x = 0; x < width; x++) {
-        lum = (rowBuffer[x >> 3] & (0x80 >> (x & 7))) ? 0xFF : 0x00;
+        // Get palette index (0 or 1) from bit at position x
+        const uint8_t palIndex = (rowBuffer[x >> 3] & (0x80 >> (x & 7))) ? 1 : 0;
+        // Use palette lookup for proper black/white mapping
+        lum = paletteLum[palIndex];
         packPixel(lum);
       }
       break;