feat: add OpenTelemetry log and metric projectors

[imran-siddique]

Summary

• emit normalized governance events through caller-owned OpenTelemetry Loggers
• add bounded-cardinality policy, approval, data-flow, token, and cost metrics
• preserve per-agent/per-workflow detail in structured logs instead of metric labels
• reject context mismatches before durable evidence persistence

Evidence

• focused projector/evidence tests: 16 passed
• full suite: 47 passed, 15 subtests passed
• real OpenTelemetry SDK in-memory Logs and Metrics exporters exercised
• schema, version, conformance, compile, build, and wheel gates pass

Limits

• no provider/exporter installation
• collector/backend interoperability remains future work
• unallowlisted classification values collapse to _other