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>

lib/GfxRenderer/FontCacheManager.cpp

@@ -2,18 +2,35 @@
 
 #include <FontDecompressor.h>
 #include <Logging.h>
+#include <SdCardFont.h>
 
 #include <cstring>
 
-FontCacheManager::FontCacheManager(const std::map<int, EpdFontFamily>& fontMap) : fontMap_(fontMap) {}
+FontCacheManager::FontCacheManager(const std::map<int, EpdFontFamily>& fontMap,
+                                   const std::map<int, SdCardFont*>& sdCardFonts)
+    : fontMap_(fontMap), sdCardFonts_(sdCardFonts) {}
 
 void FontCacheManager::setFontDecompressor(FontDecompressor* d) { fontDecompressor_ = d; }
 
 void FontCacheManager::clearCache() {
   if (fontDecompressor_) fontDecompressor_->clearCache();
+  for (auto& [id, font] : sdCardFonts_) {
+    font->clearCache();
+  }
 }
 
 void FontCacheManager::prewarmCache(int fontId, const char* utf8Text, uint8_t styleMask) {
+  // SD card font prewarm path: prewarm all requested styles in one call
+  auto it = sdCardFonts_.find(fontId);
+  if (it != sdCardFonts_.end()) {
+    int missed = it->second->prewarm(utf8Text, styleMask);
+    if (missed > 0) {
+      LOG_DBG("FCM", "prewarmCache(SD): %d glyph(s) not found (styleMask=0x%02X)", missed, styleMask);
+    }
+    return;
+  }
+
+  // Standard compressed font prewarm path: loop over all requested styles
   if (!fontDecompressor_ || fontMap_.count(fontId) == 0) return;
 
   for (uint8_t i = 0; i < 4; i++) {
@@ -30,10 +47,16 @@ void FontCacheManager::prewarmCache(int fontId, const char* utf8Text, uint8_t st
 
 void FontCacheManager::logStats(const char* label) {
   if (fontDecompressor_) fontDecompressor_->logStats(label);
+  for (auto& [id, font] : sdCardFonts_) {
+    font->logStats(label);
+  }
 }
 
 void FontCacheManager::resetStats() {
   if (fontDecompressor_) fontDecompressor_->resetStats();
+  for (auto& [id, font] : sdCardFonts_) {
+    font->resetStats();
+  }
 }
 
 bool FontCacheManager::isScanning() const { return scanMode_ == ScanMode::Scanning; }