Package a signed helper app

[TheGuyWithoutH]

Summary

Plan and implement a signed macOS helper app as the next packaging tier beyond the current unsigned alpha.

Why

A signed helper app is the cleanest long-term path for stable macOS permissions and a better installation story.

Scope

• Define the helper-app packaging shape.
• Choose how the MCP server launches or communicates with the helper.
• Document the migration path from the current unsigned source-install approach.

Acceptance Criteria

• The packaging approach is documented.
• The implementation path is broken down enough to execute in future PRs.