docs: Actualizar REFERENCE.md con API TTF completa

- Reemplazar nota de placeholder con documentación real
- Añadir ejemplos de código para cargar y usar TTF
- Documentar FontRef para API unificada bitmap/TTF
- Listar fuentes recomendadas con rutas en Fedora
- Documentar features: AA, cache, alpha blending

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

REFERENCE.md

@@ -645,20 +645,60 @@ renderer.setDefaultFont(@constCast(&render.font_8x16_latin1));
 ```
 
 **TrueType Fonts** (`src/render/ttf.zig`):
+
+TTF fonts are fully supported with real glyph rasterization and antialiasing.
+
 ```zig
 const TtfFont = zcatgui.render.TtfFont;
+const FontRef = zcatgui.render.FontRef;
 
-var ttf = try TtfFont.loadFromFile(allocator, "font.ttf");
+// Load TTF from file
+var ttf = try TtfFont.loadFromFile(allocator, "/usr/share/fonts/adwaita-sans-fonts/AdwaitaSans-Regular.ttf");
 defer ttf.deinit();
 
-ttf.setSize(16);  // Set render size
+// Set render size (glyphs cached per size)
+ttf.setSize(14);  // 14pt
+
+// Get metrics
 const metrics = ttf.getGlyphMetrics('A');
-ttf.textWidth("Hello");
+const width = ttf.textWidth("Hello");
+const height = ttf.lineHeight();
+const asc = ttf.ascent();   // Baseline to top
+const desc = ttf.descent(); // Baseline to bottom
+
+// Draw text directly
+ttf.drawText(&framebuffer, x, y, "¡Hola, España!", color, clip);
+
+// Or use FontRef for unified bitmap/TTF API
+const font_ref = FontRef{ .ttf = &ttf };
+font_ref.drawText(&framebuffer, x, y, "Hello", color, clip);
 ```
 
-> **Note**: TTF rendering currently uses placeholder glyphs. Full TTF rasterization
+**Features:**
-> (bezier curve rendering) is planned for future releases. For production use,
+- Real bezier curve rasterization (quadratic beziers)
-> prefer the bitmap fonts which have complete glyph rendering.
+- Antialiasing via 2x supersampling
+- Glyph caching (by codepoint + size)
+- Alpha blending for smooth edges
+- Full Unicode support (BMP via cmap format 4, full via format 12)
+
+**Recommended fonts (free, good Latin-1 support):**
+| Font | Location (Fedora) | Notes |
+|------|-------------------|-------|
+| AdwaitaSans | `/usr/share/fonts/adwaita-sans-fonts/` | GNOME default, modern |
+| DejaVu Sans | `/usr/share/fonts/dejavu-sans-fonts/` | Very complete |
+| Droid Sans | `/usr/share/fonts/google-droid-sans-fonts/` | Android default |
+
+**Switching between Bitmap and TTF:**
+```zig
+// Use FontRef to switch fonts without changing widget code
+var current_font: FontRef = .{ .bitmap = &render.font_8x16_latin1 };
+
+// Later, switch to TTF
+current_font = .{ .ttf = &ttf_font };
+
+// Widget code stays the same
+current_font.drawText(fb, x, y, text, color, clip);
+```
 
 ### UTF-8 Text Rendering