feat(observability): add structured lifecycle receipts

[offendingcommit]

Summary

This is the shared-contract part of the video observability work. Hermes core now distinguishes tool failures from failed operations; this PR gives plugins a common local event format; Sirens can then emit comparable Daphne and DJ Doot generation lifecycles without inventing its own logging contract.

Plugins can correlate multi-stage work through ObservabilityEvent and log_observability_event. The v1 schema carries request, persona, provider, credential-identity, stage, retry, error, timing, and artifact metadata while omitting null fields.

The logger has no exporter or outbound telemetry. It bounds payloads, recursively redacts secret-looking attributes, scrubs common inline credentials, escapes control characters, and offers a domain-separated credential identity hash so operators can compare wiring without exposing keys.

Validation

• make test — 111 passed, 10 expected Hermes contract skips
• make build — source distribution and wheel built; the wheel includes observability.py
• uv run python -m compileall -q hermes_plugin_kit tests
• git diff --check

Related

The Sirens consumer PR is being developed in parallel and will pin this package to an immutable merge commit before deployment.