feat: add Bounty Analytics Dashboard with charts, stats, and CSV export (Closes #859) [fj4WqyCCw3C5ShR1RfB7MoBPTpkRrBFYP1uT35g3MvT]

[waterWang]

Summary

Implements the Bounty Analytics Dashboard (#859) — a comprehensive analytics dashboard for tracking bounty trends, payout distribution, contributor growth, and engagement metrics with exportable reports.

Changes

New: AnalyticsPage

• Summary Stats Cards — Open Bounties, Total Paid, Contributors, Total Bounties with period-over-period trend indicators
• Bounty Volume Chart — Area chart showing created vs completed bounties over time
• Status Distribution — Donut chart showing bounty status breakdown
• Tier Distribution — Bar chart showing bounties by tier level
• Average Reward by Tier — Bar chart with average reward amounts per tier
• Top Skills — Horizontal bar chart showing most requested skills
• Daily Submissions — Line chart showing submission activity over time
• Token Distribution — Donut chart showing reward token distribution

CSV Export

• Export bounty list as CSV
• Export volume data as CSV
• Export contributor leaderboard as CSV

Other

• Added Analytics to nav bar with active indicator
• Added route for /analytics
• Restored missing lib/animations.ts and lib/utils.ts modules

Technical Details

• Uses Recharts for all chart visualizations
• Client-side data processing from existing API endpoints
• Period selector (7d / 30d / 90d / All time) for filtering data
• Dark theme matching SolFoundry's Forge design system
• Framer Motion animations for smooth transitions

Acceptance Criteria

• Time-series charts for bounty volume and payouts
• Contributor growth and retention metrics
• Exportable reports (CSV)
• Responsive layout for all screen sizes
• Dark theme consistency