Add windowed leaderboard and transparency APIs

[Quanwritescodes]

Summary

This PR adds the missing public visibility and historical tracking needed for solver performance, slash transparency, and protocol reporting.

What changed

1) Windowed solver leaderboard history

• Added a new GET /api/v1/solvers/leaderboard?window=24h|7d|30d|all endpoint.
• Rankings are computed over the requested window instead of showing only the current all-time snapshot.
• The legacy GET /api/v1/solvers all-time endpoint remains intact for compatibility.
• Solver stats now support windowed reputation calculations at GET /api/v1/solvers/:address/stats?window=....

2) Slash history and dispute workflow

• Slashes are now persisted in a structured solver history record when a missed fill is slashed.
• Added GET /api/v1/solvers/:address/slashes with pagination.
• Added POST /api/v1/solvers/:address/slashes/:slashId/dispute with signature validation using the repo's Stellar-signature pattern.
• Added manual dispute resolution support for resolved-upheld and resolved-reversed outcomes.

3) Public protocol transparency endpoint

• Added GET /api/v1/stats/public.
• The response includes:
  • total/open/filled intent counts
  • total volume
  • per-SupportedChain intent counts and volume
  • active solver count
  • WS subscriber count
  • version metadata for a stable public contract
• Added a design note at docs/public-transparency-contract.md describing the stable contract policy.

Why this matters

These changes improve the protocol's transparency in the same way a real public reputation system should: they allow recent performance to be evaluated separately from historical activity, make slashing auditable, and give the community a stable public reference surface for dashboards and reporting.

Notes

• This work intentionally preserves the existing all-time leaderboard and legacy stats behavior.
• No broad validation run was performed as part of this scoped change set.

closes #249
closes #250
closes #251
closes #252

[drips-wave]

@Quanwritescodes Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits