Adds read-only `compare` command that fetches both the remote Outline
instance (via Tailscale) and a local instance (outline-web container),
matches documents by canonical path key, and reports in_sync / remote_only /
local_only / conflict status. Also adds PRD for the full two-instance sync
workflow.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
