feat: Add JSON-based font configuration system

[NekoEpisode]

Summary

Implemented a flexible font configuration system for easy multi-language support through external JSON config. Fonts are now loaded from fonts/config.json instead of being hardcoded.

Key Features

• Declarative config: Add new fonts by editing JSON, no code changes needed
• Multi-language support: Easy to add Chinese, Japanese, Korean, etc.
• Flexible sizing: Supports both fixed-width and variable-width fonts
• ID-based lookup: Access fonts by ID for special rendering needs
• Auto-fallback: Missing characters automatically use default font

Configuration Format

{
  "font_files": {
    "default": {
      "path": "/fonts/default/font.png",
      "chars": ["ABC", "123", "..."],
      "char_size_type": "array",
      "char_size_array": [3, 2, 4, ...],
      "h_space": 2
    },
    "zh_cn_1": {
      "path": "/fonts/zh_cn/font.png",
      "chars": ["汉字", "..."],
      "char_size_type": "fixed",
      "char_size": 8,                      // Use 8 for CJK fonts
      "h_space": 2
    }
  }
}

⚠️ CRITICAL: Path Requirements

Font paths MUST begin with "/" or the game will not load the font correctly!

Correct: "path": "/fonts/default/font.png"
Wrong:   "path": "fonts/default/font.png"

Character Size Guidelines

• Latin/proportional fonts: Use "char_size_type": "array" with individual widths
• CJK fonts: Use "char_size_type": "fixed" with "char_size": 8

Changes

• Added FontRenderer.setDefaultFont() for delayed initialization
• Added fontById HashMap for O(1) font lookup by ID
• Added loadFonts() method in LWJGLWindow to parse JSON config
• Removed hardcoded font initialization from constructor
• All fonts now loaded at startup with comprehensive error handling

Usage

// Fonts auto-load from config at startup
fontRenderer.drawString(x, y, scale, scale, "Hello 世界");

// Check if font exists
if (fontRenderer.hasFontId("japanese")) { ... }