Adds admin's own documents, its unique indexes and the plan seed from
shared/license.
Licences are append-only -- a renewal writes a new row and supersedes the
old one -- because the history is the support tool. Plans are seeded with
$setOnInsert only, so a redeploy never stamps over staff edits to limits,
features or Paddle IDs.
admin_instances.instance_id unique is a correctness property, not an
optimisation: without it two customers could both claim one self-hosted
UUID and both be issued licences for it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>