feature: Add 'Copy Comparison as Markdown Table' button for GitHub Discussions #226

Add a 'Copy as Markdown' action button in the comparison dashboard. When clicked, it generates and copies a clean GitHub-flavored markdown table comparing the two developers, complete with scores, metrics, winner badge, and an attribution link back to DevImpact.

Motivation

Developers frequently discuss tools and open-source contributions in GitHub Issues, Pull Request reviews, and Discord/Slack channels. When they paste DevImpact markdown tables, the built-in attribution link ('Analyzed via DevImpact') spreads the repo directly across GitHub.

Tasks

• Implement a helper function formatComparisonToMarkdown(user1, user2, winner) that outputs a clean Markdown table with metrics and score breakdown.
• Add a 'Copy as Markdown' button alongside existing action buttons in ResultDashboard.
• Connect with useClipboardCopy hook to provide immediate visual feedback (e.g., checkmark and 'Copied!').
• Include an attribution line at the bottom: _Generated with [DevImpact](https://github.com/O2sa/DevImpact)_.
• Add a unit test verifying the markdown formatting output.

Files to Check

• src/features/comparison/components/result-dashboard.tsx
• src/hooks/use-clipboard-copy.ts