docs(api): enhance OpenAPI spec with complete endpoint documentation

- Added /api/stats endpoint for network statistics
- Added /api/hall_of_fame endpoint for leaderboard (5 categories)
- Added /api/fee_pool endpoint for RIP-301 fee pool stats
- Added /wallet/transfer (admin) endpoint
- Added /withdraw/request endpoint
- Added /explorer endpoint
- Added Network and Explorer tags
- Updated request/response schemas with detailed descriptions

Bounty: Scottcjn#502 OpenAPI/Swagger Documentation for Node API (30 RTC)

Author: sososonia-cyber