feat: add Agentic Observatory contracts and trace queries

[Svaag]

Summary

• add shared Agentic Observatory DTOs for loops, timelines, cases, handoffs, verification, Knowledge artifacts, topology, actions, and change-impact reports
• extend TraceEvent with optional observatory correlation fields while preserving backward compatibility
• add collector read/query endpoints for loops, runs, run events, actions, topology, and daily metrics

Validation

• .venv/bin/ruff check agent_core tests
• .venv/bin/mypy agent_core
• .venv/bin/pytest -q