# Cherry-pick Image Support from pablohc/crosspoint-reader@2d8cbcf (PR #556)

## Task
Merge EPUB embedded image support (JPEG/PNG) from pablohc's fork into the mod branch, based on upstream PR #556.

## Changes Made

### New Files (11)
- `lib/Epub/Epub/blocks/ImageBlock.h` / `.cpp` - Image block type for page layout
- `lib/Epub/Epub/converters/DitherUtils.h` - 4x4 Bayer dithering for 4-level grayscale
- `lib/Epub/Epub/converters/ImageDecoderFactory.h` / `.cpp` - Format-based decoder selection
- `lib/Epub/Epub/converters/ImageToFramebufferDecoder.h` / `.cpp` - Base decoder interface
- `lib/Epub/Epub/converters/JpegToFramebufferConverter.h` / `.cpp` - JPEG decoder (picojpeg)
- `lib/Epub/Epub/converters/PngToFramebufferConverter.h` / `.cpp` - PNG decoder (PNGdec)
- `lib/Epub/Epub/converters/PixelCache.h` - 2-bit pixel cache for fast re-render
- `scripts/generate_test_epub.py` - Test EPUB generator

### Modified Files (13)
- `lib/Epub/Epub/blocks/Block.h` - Removed unused `layout()` virtual
- `lib/Epub/Epub/blocks/TextBlock.h` - Removed unused `layout()` override
- `lib/Epub/Epub/Page.h` / `.cpp` - Added `PageImage` class, `TAG_PageImage=3`, `hasImages()`, `getImageBoundingBox()`
- `lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h` / `.cpp` - Image extraction/decoding from EPUB, new constructor params
- `lib/Epub/Epub/Section.cpp` - Derive content base/image paths, bumped version 12→13
- `lib/GfxRenderer/GfxRenderer.h` / `.cpp` - Added `getRenderMode()`, implemented `displayWindow()`
- `lib/hal/HalDisplay.h` / `.cpp` - Added `displayWindow()` for partial refresh
- `src/activities/reader/EpubReaderActivity.cpp` - Image-aware refresh with double FAST_REFRESH optimization
- `platformio.ini` - Added `PNGdec` dependency, `PNG_MAX_BUFFERED_PIXELS=6402` build flag

## Key Conflict Resolutions
- `TAG_PageImage = 3` (not 2) to avoid collision with mod's `TAG_PageTableRow = 2`
- Preserved mod's bookmark ribbon rendering in `renderContents`
- Preserved mod's table rendering (`PageTableRow`) alongside new `PageImage`
- Section file version bumped to invalidate cached sections

## Build Result
- `mod` environment: SUCCESS (RAM 31.0%, Flash 77.5%)

## Follow-up Items
- Test on device with JPEG/PNG EPUBs
- Run `scripts/generate_test_epub.py` to create test EPUBs
- Consider whether `displayWindow()` experimental path should be enabled