feat: add phase 1 evaluator tracing for OpenCode

[zwobill]

Summary

• Add evaluator correlation context to the existing OpenCode tracer.
• Track evaluator/verifier session roles through the existing session graph.
• Enforce evaluator tool allow-lists at the existing tool hook boundary.
• Capture valid, malformed, and missing scorecard output without mutating subject traces.

Verification

• npm test in packages/opencode-plugin (64 passed)
• npm run typecheck
• npm run build

The plugin does not implement SOP reasoning or a second tracing/configuration system.