Display book cover image as background in the Continue Reading card on
the home screen, improving visual identification of the current book.
Key changes:
- Add thumbnail generation (thumb.bmp) for EPUB and XTC/XTCH files
- Uses same dithering/scaling algorithms as sleep screen covers
- Target size: 240x400 (half screen) for optimal Continue Reading card fit
- Add JpegToBmpConverter::jpegFileToBmpStreamWithSize() for custom target sizes
- Add GfxRenderer::copyStoredBwBuffer() and freeStoredBwBuffer() for
framebuffer caching to maintain fast navigation performance
- Add UTF-8 safe string truncation for Korean/CJK text in title/author display
- Draw white boxes behind title/author text for readability over cover image
- Increase HomeActivityTask stack size to 4096 for cover image rendering
- Add bounds checking in XTC thumbnail generation to prevent buffer overflow
## Summary
* Swap to updated SDCardManager which uses SdFat
* Add exFAT support
* Swap to using FsFile everywhere
* Use newly exposed `SdMan` macro to get to static instance of
SDCardManager
* Move a bunch of FsHelpers up to SDCardManager
## Summary
* **What is the goal of this PR?**
Replace simple threshold-based grayscale quantization with ordered
dithering using a 4x4 Bayer matrix. This eliminates color banding
artifacts and produces smoother gradients on e-ink display.
* **What changes are included?**
- Add 4x4 Bayer dithering matrix for 16-level threshold patterns
- Modify `grayscaleTo2Bit()` function to accept pixel coordinates and
apply position-based dithering
- Replace simple `grayscale >> 6` threshold with ordered dithering
algorithm that produces smoother gradients
## Additional Context
* Bayer matrix approach: The 4x4 Bayer matrix creates a repeating
pattern that distributes quantization error spatially, effectively
simulating 16 levels of gray using only 4 actual color levels (black,
dark gray, light gray, white).
* Cache invalidation: Existing cached `cover.bmp` files will need to be
deleted to see the improved rendering, as the converter only runs when
the cache is missing.
## Summary
* Handle 16x16 MCU blocks in JPEG decoding
* We were only correctly handling 8x8 blocks, which means that we did
not correctly support a lot of JPGs leading to an interlacing style on
the images
## Additional Context
* Fixes https://github.com/daveallie/crosspoint-reader/issues/118
## Summary
- Add basic JPG image support
- Map JPG back to 2-bit BMP output
- Can be used to later render the BMP file from disk or directly pass to
output if wanted
- Give the 3 passes over the data needed to render grayscale content,
putting it on disk is preferred to outputting it multiple times
## Additional Context
- WIP, looking forward to BMP support from
https://github.com/daveallie/crosspoint-reader/pull/16
- Addresses some of #11
