spec(events): freeze v1 event names/params and publish indexer mapping notes

[rosspeili]

Summary

Stabilize event schema between docs and Solidity interfaces.

Why

Indexers/subgraphs need event stability to integrate early.

Scope

• Reconcile events-v1.md with Solidity event definitions
• Confirm indexed fields for query efficiency
• Add versioning/changelog notes for event changes

Acceptance Criteria

• Docs and interface events match exactly
• Indexer guidance includes key correlation fields