v0.1.0-rc.1

Fixed

• Reject an empty pinned-engine set instead of falling back to SearXNG
  categories, which could fan out to every enabled engine and overload the
  private instance.
• Align the public, operator, and agent documentation with v0.1.0-rc.1, the
  production Vido bridge, the single physical core-postgres deployment, and
  the complete Searchy × Vido RC smoke gate.