Normalize MCP lifecycle events

[Genmin]

Summary

• adds MCP lifecycle event normalization helpers for resource reads, prompt gets, tool results, and policy decisions
• wires normalized mcp_events into MCP workflow trace construction while preserving existing events behavior
• carries server-scoped metadata such as server_id, trust, transport, server identity, protocol version, canonical MCP tool names, and policy decisions
• documents the normalized event shapes in both the MCP adapter design and trace format docs

Validation

• python -m pytest tests/test_mcp_adapter.py -q
• python -m pytest -q
• python -m compileall -q src/agent_harness/mcp_adapter.py
• git diff --check

Closes #97.