Prototype macOS menu bar app for Runme agent

[jlewi]

Summary

• add an experimental Swift macOS menu bar app at experimental/macos/runme-menu
• add process supervision for runme agent serve with status, open UI, and log access
• add bundling support to build/copy the runme binary into app resources
• add multi-config menu behavior: discover config*.yaml in ~/.runme-agent, render one submenu per config, and expose Start/Stop/Open UI/Open Log per config
• keep prototype in single-active-config mode to avoid port conflicts by default

Validation

• swift build (for experimental/macos/runme-menu) passes
• runme run lint test: lint passes; test fails in this environment due pre-existing tooling/env issues (e.g. z prompt injection and missing tools like tree/digest/deno), unrelated to these Swift changes

Notes

• this is prototype-only and not yet integrated with login items, notarization, or release packaging