feat: add SD card font support with on-device download and web management

Add a complete SD card font subsystem that enables users to install and
use custom fonts beyond the three built-in families. This combines the
back-end firmware support (#1327) with the font configuration, build
pipeline, CI distribution, and user-facing management UI (#1392).

Core font system:
- Custom .cpfont binary format (v4) with multi-style support (regular,
  bold, italic, bold-italic) packed into a single file per size
- On-demand glyph loading from SD card with two-pass prewarm rendering
  to bulk-read glyphs per page, achieving near-flash performance for
  Latin text (~697ms vs ~681ms) and viable CJK rendering (~32% slower)
- Persistent advance cache for layout measurement without SD I/O
- Overflow ring buffer for glyph cache misses during rendering
- Memory-conscious design: only advance tables kept in RAM; glyph
  bitmaps, kern tables, and ligatures loaded on demand from SD

Font management:
- On-device WiFi download from GitHub Releases with manifest-based
  discovery, install/update detection, and progress UI
- Web interface font upload, listing, and deletion via /fonts page
- Manual SD card copy to /fonts/ or /.fonts/ directories
- Font selection integrated into Settings > Reader > Font Family

Build pipeline:
- Declarative YAML config (sd-fonts.yaml) as single source of truth
  for the 17-family font library (serif, sans, mono, accessibility)
- Python converter (fontconvert_sdcard.py) for TTF/OTF to .cpfont with
  FreeType rasterization, class-based kerning, and ligature extraction
- Parallel build orchestrator with variable font instance extraction
- CI workflow publishing versioned + stable releases to a dedicated
  crosspoint-fonts repository with auto-incrementing revision tags
- Centralized version constants (cpfont_version.py) shared across
  build tooling and CI, with firmware headers as manual sync points

Additional fixes:
- CJK characters no longer get hyphens inserted at line breaks
- Advance table eliminates 30+ second stalls during CJK section
  indexing for paragraphs with >512 unique codepoints

Closes #930

Co-authored-by: Zach Nelson <zach@zdnelson.com>
Co-authored-by: Justin <itsthisjustin@users.noreply.github.com>
Co-authored-by: jpirnay <jens@pirnay.com>
Co-authored-by: mcrosson <kemonine@kemonine.info>

src/components/themes/BaseTheme.cpp

@@ -231,7 +231,8 @@ void BaseTheme::drawList(const GfxRenderer& renderer, Rect rect, int itemCount,
                          const std::function<std::string(int index)>& rowTitle,
                          const std::function<std::string(int index)>& rowSubtitle,
                          const std::function<UIIcon(int index)>& rowIcon,
-                         const std::function<std::string(int index)>& rowValue, bool highlightValue) const {
+                         const std::function<std::string(int index)>& rowValue, bool highlightValue,
+                         const std::function<bool(int index)>& rowDimmed) const {
   int rowHeight =
       (rowSubtitle != nullptr) ? BaseMetrics::values.listWithSubtitleRowHeight : BaseMetrics::values.listRowHeight;
   int pageItems = rect.height / rowHeight;
@@ -279,6 +280,16 @@ void BaseTheme::drawList(const GfxRenderer& renderer, Rect rect, int itemCount,
     auto item = renderer.truncatedText(font, itemName.c_str(), textWidth);
     renderer.drawText(font, rect.x + BaseMetrics::values.contentSidePadding, itemY, item.c_str(), i != selectedIndex);
 
+    // Apply checkerboard dither to create gray text effect for dimmed items
+    if (rowDimmed && rowDimmed(i) && i != selectedIndex) {
+      const int titleWidth = renderer.getTextWidth(font, item.c_str());
+      const int lineH = renderer.getLineHeight(font);
+      const int tx = rect.x + BaseMetrics::values.contentSidePadding;
+      for (int py = itemY; py < itemY + lineH; py++)
+        for (int px = tx; px < tx + titleWidth; px++)
+          if ((px + py) % 2 == 0) renderer.drawPixel(px, py, false);
+    }
+
     if (rowSubtitle != nullptr) {
       // Draw subtitle
       std::string subtitleText = rowSubtitle(i);