Add AnsiRenderer for terminal output

[dereuromark]

Summary

Adds a new AnsiRenderer that outputs ANSI-formatted text for terminal display. This is inspired by tjot, a terminal renderer for Djot.

Features

• Colored headings - Different colors per level, h1/h2 get underlines
• Text styling - Bold, italic, underline, strikethrough via ANSI codes
• Colored inline code - Yellow highlighting
• Unicode tables - Box-drawing characters (┌─┬─┐ etc.)
• Blockquote bars - Colored │ prefix
• List bullets - • for unordered, numbers for ordered
• Task checkboxes - ☑ (checked) / ☐ (unchecked)
• Super/subscript - Unicode characters (² ₂)
• Symbols to emoji - ❤️ → ❤
• Configurable - Colors, Unicode, terminal width

Use Cases

• CLI documentation viewers
• Terminal-based Djot editors/previewers
• Developer tooling (show formatted help)
• README previews in terminal

Example Usage

use Djot\DjotConverter;
use Djot\Renderer\AnsiRenderer;

$converter = new DjotConverter();
$renderer = new AnsiRenderer();

$document = $converter->parse($djotContent);
echo $renderer->render($document);

Example Output

Run php examples/ansi-demo.php to see:

Text preview (without colors)

Welcome to Djot
═══════════════

Djot is a lightweight markup language with emphasis, strong, and inline code.

Features
────────

• Highlighted text for important notes
• Inserted and deleted text
• Superscript: E=mc²
• Subscript: H₂O
• Symbols: I ❤ Djot!

Tables
──────

┌──────────────┬──────────┬──────┐
│ Feature      │ Markdown │ Djot │
├──────────────┼──────────┼──────┤
│ Highlighting │ No       │ Yes  │
│ Attributes   │ No       │ Yes  │
└──────────────┴──────────┴──────┘

Configuration

$renderer = new AnsiRenderer(
    terminalWidth: 120,  // For line wrapping
    useColors: true,     // ANSI color codes
    useUnicode: true,    // Unicode bullets/boxes
);

// Or fluent:
$renderer
    ->setTerminalWidth(80)
    ->setUseColors(false)  // Plain text fallback
    ->setUseUnicode(false); // ASCII fallback

[codecov]

Codecov Report

❌ Patch coverage is 86.21701% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.84%. Comparing base (ec22f0f) to head (142ff6c).
⚠️ Report is 56 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Renderer/AnsiRenderer.php	86.21%	47 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #13      +/-   ##
============================================
- Coverage     93.35%   92.84%   -0.51%     
- Complexity     1631     1789     +158     
============================================
  Files            59       60       +1     
  Lines          4258     4599     +341     
============================================
+ Hits           3975     4270     +295     
- Misses          283      329      +46     

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