Add AnsiRenderer for terminal output

Adds a new renderer that outputs ANSI-formatted text for terminal display.

Features:
- Colored headings (different colors per level, underlined h1/h2)
- Bold, italic, underline, strikethrough styling
- Colored inline code
- Unicode box-drawing for tables
- Blockquote bars with color
- Bullet points (• or * fallback)
- Task list checkboxes (☑/☐)
- Super/subscript using Unicode characters
- Symbol to emoji mapping (:heart: → ❤)
- Configurable: colors, Unicode, terminal width

Use cases:
- CLI documentation viewers
- Terminal-based Djot editors
- Developer tooling
- README previews in terminal

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

Author: dereuromark

examples/ansi-demo.php

@@ -0,0 +1,89 @@
+#!/usr/bin/env php
+<?php
+
+/**
+ * ANSI Renderer Demo
+ *
+ * Run this script in a terminal to see colorized Djot output:
+ *   php examples/ansi-demo.php
+ */
+
+declare(strict_types=1);
+
+require __DIR__ . '/../vendor/autoload.php';
+
+use Djot\DjotConverter;
+use Djot\Renderer\AnsiRenderer;
+
+$djot = <<<'DJOT'
+# Welcome to Djot
+
+Djot is a lightweight markup language with _emphasis_, *strong*, and `inline code`.
+
+## Features
+
+- {=Highlighted text=} for important notes
+- {+Inserted+} and {-deleted-} text
+- Superscript: E=mc{^2^}
+- Subscript: H{~2~}O
+- Symbols: I :heart: Djot!
+
+## Code Example
+
+```php
+$converter = new DjotConverter();
+echo $converter->convert($djot);
+```
+
+## Links and Images
+
+Visit [the Djot website](https://djot.net) for more info.
+
+![A sample image](photo.jpg)
+
+## Blockquotes
+
+> Djot is designed to be parsed without backtracking,
+> making it fast and predictable.
+>
+> — John MacFarlane
+
+## Tables
+
+| Feature      | Markdown | Djot |
+|--------------|----------|------|
+| Highlighting | No       | Yes  |
+| Attributes   | No       | Yes  |
+| Consistent   | No       | Yes  |
+
+## Definition List
+
+: Djot
+  A modern markup language designed for clarity.
+
+: Markdown
+  The predecessor with many flavors.
+
+## Task List
+
+- [ ] Learn Djot syntax
+- [x] Install djot-php
+- [ ] Build something awesome
+
+---
+
+## Footnotes
+
+Here's a statement with a footnote[^1].
+
+[^1]: This is the footnote content.
+DJOT;
+
+$converter = new DjotConverter();
+$renderer = new AnsiRenderer();
+
+// Parse and render
+$document = $converter->parse($djot);
+$output = $renderer->render($document);
+
+echo $output;