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/EpdFont/SdCardFontManager.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+class GfxRenderer;
+class SdCardFont;
+struct SdCardFontFamilyInfo;
+
+class SdCardFontManager {
+ public:
+  SdCardFontManager() = default;
+  ~SdCardFontManager();
+  SdCardFontManager(const SdCardFontManager&) = delete;
+  SdCardFontManager& operator=(const SdCardFontManager&) = delete;
+
+  // Load the font file matching fontSizeEnum (SMALL=0 .. EXTRA_LARGE=3) by
+  // ordinal position in the family's sorted size list. Only one .cpfont file
+  // is loaded; other sizes remain on disk. This keeps resident interval +
+  // kern/ligature tables to one size's worth of memory.
+  // Returns true on success.
+  bool loadFamily(const SdCardFontFamilyInfo& family, GfxRenderer& renderer, uint8_t fontSizeEnum);
+
+  // Unload everything, unregister from renderer.
+  void unloadAll(GfxRenderer& renderer);
+
+  // Look up the font ID for the loaded family. Returns 0 if nothing loaded
+  // or familyName doesn't match.
+  int getFontId(const std::string& familyName) const;
+
+  // Get name of currently loaded family (empty if none).
+  const std::string& currentFamilyName() const { return loadedFamilyName_; };
+
+  // Point size that was actually loaded (closest match to targetPtSize).
+  // 0 if nothing loaded.
+  uint8_t currentPointSize() const { return loadedPointSize_; };
+
+ private:
+  struct LoadedFont {
+    SdCardFont* font;  // heap-allocated, owned
+    int fontId;
+    uint8_t size;
+  };
+  static int computeFontId(uint32_t contentHash, const char* familyName, uint8_t pointSize);
+
+  std::string loadedFamilyName_;
+  uint8_t loadedPointSize_ = 0;
+  std::vector<LoadedFont> loaded_;
+};