Document one-command workstation convergence

[priithunt]

What changed

• describe the single M3 convergence command as the normal daily path
• explain automatic source reconciliation and approval-based Intel action selection
• document resumable offline secondary handling and one-time status resolution

Why

The public showcase should match the private workstation workflow after P2: normal two-Mac changes no longer require copying separate publish, apply, and rollout commands.

Validation

• private curated snapshot check passed for all 44 allowlisted files
• public scripts/verify-showcase.sh . passed
• private Gitea, private GitHub, M3, and Intel converged to the same P2 closeout commit