Add projection runtime MCP contract

[IYENTeam]

Summary

• add projection MCP request/response types and persistence storage under projections/
• expose projection enqueue/list/get/search/refresh tools from the phronesis MCP server
• add projection persistence tests and harden source path validation and agent-scoped artifact identity

Verification

• cargo test
• cargo check

Cross-repo dependency

• companion MemoryOwn PR consumes this MCP contract for projection runtime integration