feat: Add markdown to ADF (Atlassian Document Format) adapter module

[codegen-sh]

Overview

This PR adds a comprehensive markdown to ADF (Atlassian Document Format) adapter module to the Codegen backend. The adapter converts standard Markdown text to ADF JSON structure, which is used by Atlassian products like Jira and Confluence.

What's Added

📦 New Module: src/codegen/shared/markdown_adf/

• adapter.py - Main MarkdownToADFAdapter class with conversion logic
• adf_types.py - Comprehensive type definitions for ADF document structure
• __init__.py - Module exports and public API
• README.md - Detailed documentation with usage examples

🧪 Comprehensive Test Suite

• tests/shared/test_markdown_adf_adapter.py - 20+ test cases covering:
  • Basic text and paragraph conversion
  • Headings (H1-H6)
  • Inline formatting (bold, italic, code, links, strikethrough)
  • Code blocks with language detection
  • Lists (bullet and ordered)
  • Blockquotes and horizontal rules
  • Complex nested structures
  • Error handling and edge cases

📋 Dependencies

• Added markdown>=3.4.0 to pyproject.toml

Supported Markdown Elements

Markdown	ADF Node/Mark	Description
# Heading	heading	Headings H1-H6
**bold**	strong mark	Bold text
*italic*	em mark	Italic text
`code`	code mark	Inline code
[link](url)	link mark	Hyperlinks
code	codeBlock	Code blocks with language detection
- item	bulletList	Bullet lists
1. item	orderedList	Numbered lists
> quote	blockquote	Block quotes
---	rule	Horizontal rules

Usage Example

from codegen.shared.markdown_adf import MarkdownToADFAdapter

adapter = MarkdownToADFAdapter()

markdown = """
# Hello World

This is a paragraph with **bold** and *italic* text.

```python
def greet(name):
    print(f"Hello, {name}!")

• Item 1
• Item 2
  """

adf_document = adapter.convert(markdown)

Returns properly structured ADF JSON

## Key Features

✅ **Robust Error Handling** - Gracefully handles malformed markdown  
✅ **Type Safety** - Comprehensive TypedDict definitions for ADF structure  
✅ **Language Detection** - Automatic language detection for code blocks  
✅ **Nested Structures** - Support for complex nested lists and formatting  
✅ **Extensible Design** - Easy to add support for additional markdown elements  

## Testing

All tests pass and cover:
- Basic conversion scenarios
- Complex nested structures  
- Error handling with malformed input
- Edge cases and empty input
- Mixed formatting combinations

## Future Enhancements

The module is designed to be easily extensible for:
- Table support
- Image and media handling  
- Custom ADF node types (panels, mentions, etc.)
- Configuration options for conversion behavior

---

[💻 View my work](https://codegen.sh/agent/trace/35616) • [About Codegen](https://codegen.com)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

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