Escrow guardrails pass: dispute lifecycle, timeout refunds, and fee basis points

[chemicalcommando]

Summary

This PR introduces a minimal, focused escrow flow update to satisfy the assigned dispute/refund/fee issue set.

Included

• Added dispute open path for eligible sessions.
• Added admin dispute resolution path with share validation.
• Added timeout-based auto refund for completed sessions outside dispute window.
• Added internal fee application helper using basis points (bps) for settlement paths.
• Added events for dispute open, dispute resolve, and auto refund execution.

Notes

• This change is intentionally compact and scoped to contracts/escrow/src/lib.rs.
• Contract build/test was not run in this environment because cargo is unavailable in PATH.

Closes #530
Closes #531
Closes #532
Closes #533

[drips-wave]

@chemicalcommando 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