Mock leaderboard backend for local development

[bh2smith]

Summary

Create a mock implementation of the leaderboard interface that stores data in localStorage instead of on-chain. This allows developing and testing the leaderboard UI and game-over hooks without a deployed contract.

Requirements

• Implement the same TypeScript interface as src/shared/circles/leaderboard.ts:
  • submitSoloResult(gameId, won, cardsRemaining)
  • submitVsAiResult(gameId, won)
  • fetchMyStats(gameId)
  • fetchTopLeaderboard(gameId)
• Store player stats in localStorage, keyed by game ID
• Generate mock player data for leaderboard testing (seed with fake entries)
• Auto-detect environment: use mock when outside miniapp context (no wallet), use real contract when in miniapp
• Maintain the same sorted top-100 semantics as the contract (solo: cumulative cards remaining ascending, vs-AI: net wins descending)

Design

The simplest approach: a leaderboardBackend.ts module that exports the same functions and switches implementation based on isInMiniapp(). The mock reads/writes localStorage; the real implementation calls the contract via viem.

Depends on

• Nothing — can start immediately

Blocks

• Game-over hooks
• Leaderboard UI