feat(theme): add roundedraff theme and fix sleep cover crop grid artifacts (#918)

## Summary
- Add new `roundedraff` theme.
- Fix sleep screen artifact where book cover showed grid lines in
`Cover` mode with `Crop`.

## Additional Context
## Key changes
- Added `src/components/themes/roundedraff/` theme implementation.
- Updated sleep cover rendering logic in:
  - `src/activities/boot_sleep/SleepActivity.cpp`
  - `src/activities/boot_sleep/SleepActivity.h`
- Improved cover generation/regeneration paths in:
  - `lib/Epub/Epub.cpp`
  - `lib/Epub/Epub.h`
  - `lib/Txt/Txt.cpp`
  - `lib/Txt/Txt.h`

## Verification
- Sleep screen set to Book cover
- Sleep screen cover mode set to Crop
- Confirmed grid artifacts no longer appear on cover sleep screen.

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< YES >**_

---------

Co-authored-by: CaptainFrito <yzq6x5zypy@privaterelay.appleid.com>
Co-authored-by: Zach Nelson <zach@zdnelson.com>
Co-authored-by: Uri Tauber <142022451+Uri-Tauber@users.noreply.github.com>

lib/GfxRenderer/GfxRenderer.cpp

@@ -493,6 +493,41 @@ void GfxRenderer::fillRectDither(const int x, const int y, const int width, cons
   }
 }
 
+void GfxRenderer::maskRoundedRectOutsideCorners(const int x, const int y, const int width, const int height,
+                                                const int radius, const Color color) const {
+  if (radius <= 0 || color == Color::Clear) {
+    return;
+  }
+
+  const int rr = radius - 1;
+  const int rr2 = rr * rr;
+  for (int dy = 0; dy < radius; dy++) {
+    for (int dx = 0; dx < radius; dx++) {
+      const int tx = rr - dx;
+      const int ty = rr - dy;
+      if (tx * tx + ty * ty > rr2) {
+        if (color == Color::White || color == Color::Black) {
+          bool state = color == Color::Black;
+          drawPixel(x + dx, y + dy, state);                           // top-left
+          drawPixel(x + width - 1 - dx, y + dy, state);               // top-right
+          drawPixel(x + dx, y + height - 1 - dy, state);              // bottom-left
+          drawPixel(x + width - 1 - dx, y + height - 1 - dy, state);  // bottom-right
+        } else if (color == Color::LightGray) {
+          drawPixelDither<Color::LightGray>(x + dx, y + dy);                           // top-left
+          drawPixelDither<Color::LightGray>(x + width - 1 - dx, y + dy);               // top-right
+          drawPixelDither<Color::LightGray>(x + dx, y + height - 1 - dy);              // bottom-left
+          drawPixelDither<Color::LightGray>(x + width - 1 - dx, y + height - 1 - dy);  // bottom-right
+        } else if (color == Color::DarkGray) {
+          drawPixelDither<Color::DarkGray>(x + dx, y + dy);                           // top-left
+          drawPixelDither<Color::DarkGray>(x + width - 1 - dx, y + dy);               // top-right
+          drawPixelDither<Color::DarkGray>(x + dx, y + height - 1 - dy);              // bottom-left
+          drawPixelDither<Color::DarkGray>(x + width - 1 - dx, y + height - 1 - dy);  // bottom-right
+        }
+      }
+    }
+  }
+}
+
 template <Color color>
 void GfxRenderer::fillArc(const int maxRadius, const int cx, const int cy, const int xDir, const int yDir) const {
   if (maxRadius <= 0) return;