Implement protocol extensions and observability features

[ryderstorm]

Summary

Add protocol extension support (tools, notifications, sampling) and observability to the SDD MCP server so clients can orchestrate richer workflows and operators gain insight into server behavior.

Tasks

• Implement helper tools in mcp_server/tools.py (list artifacts, create spec stub, summarize diff) with FastMCP decorators
• Build notification broadcaster in mcp_server/notifications.py to emit workspace file events
• Implement sampling orchestrator in mcp_server/sampling.py to request client-generated summaries
• Add structured logging and /mcp/health readiness endpoint in mcp_server/logging.py
• Create tests/test_tools_protocol.py covering tools, notifications, sampling, and logging signals
• Update docs/operations.md with observability guidance and sample outputs

Acceptance Criteria

• Helper tools are discoverable via FastMCP Inspector and verified by automated tests
• Notifications fire on new workspace artifacts and are covered by tests
• Sampling flow successfully requests and handles client responses in tests
• Structured logs and /mcp/health endpoint are exposed and documented for operators
• Documentation includes examples of logs/metrics and guidance on using the new capabilities