fix: convert ADF description to text for markdown/detail output

[pchuri]

📋 Summary

Fix --format markdown and default detail view outputting [object Object] instead of actual description content when using JIRA API v3.

🎯 Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

🔍 Changes Made

• Add convertAdfToText() function to recursively convert ADF (Atlassian Document Format) JSON to readable text/markdown
• Add resolveDescription() wrapper that handles both string (API v2) and ADF object (API v3) descriptions
• Apply conversion in formatIssueAsMarkdown() and displayIssueDetails()
• Supports paragraph, heading, bulletList, orderedList, codeBlock, blockquote, mention, hardBreak, rule, table, media node types

🧪 Testing

• All existing tests pass
• New tests added for new functionality (16 new test cases)
• Code coverage maintained/improved

📊 Test Results

Test Suites: 7 passed, 7 total
Tests:       116 passed, 116 total

🚀 Deployment Notes

• No special deployment steps required

📝 Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

🔗 Related Issues

• Closes [BUG] --format markdown outputs description as [object Object] #21

[github-actions]

🎉 This PR is included in version 2.3.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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