Add first deploy rehearsal checklist

[sigilabcodex]

This PR adds a first-deploy rehearsal checklist and clarifies the current restore/export posture.

Highlights:

• Adds docs/first-deploy-rehearsal.md
• Documents the local rehearsal workflow from /entry through bootstrap, setup, orders, production, and handoff
• Clarifies runtime mode and demo/real-data checks
• Notes that restore exists but backup/export creation is still a manual maintainer step
• Adds a /entry link to the rehearsal checklist

Checks:

• npm run typecheck passed
• npm run build passed

Out of scope:

• No backup/export implementation
• No procurement/inventory
• No WhatsApp
• No deploy scripting
• No QA automation