Add lifecycle management and sandbox support for MCP tools:
- McpClient: lazy start (server starts on first call_tool()),
configurable idle timeout with auto-stop, health monitoring
with automatic restart on server crash
- McpRegistry: namespace-isolated tracking of multiple MCP servers
with independent lifecycles
- SandboxPathRewriter: bi-directional file path rewriting between
host and sandbox workspaces using PathMapper
- MCPCapabilityMetadata: structured exposure of full MCP server
capabilities (tools, resources, prompts)
- MCPToolDescriptor: extended with annotations field
- MCPToolAdapter: capability_metadata property, enhanced source_metadata
with server capabilities and tool annotations
BDD scenarios:
- 16 lifecycle scenarios (lazy start, auto-stop, health check, registry)
- 10 sandbox path rewriting scenarios (arguments, responses, roundtrip)
- All 42 existing MCP adapter scenarios continue to pass
ISSUES CLOSED: #938
