XY-819: [ELF prod P0] Add single-user production runbook with backup and restore

[yvette-carlisle]

Summary:

• Add the single-user production runbook covering Compose storage, service startup, health, migration checks, backup, restore, rollback, and Qdrant rebuild proof.
• Parameterize the checked-in Compose storage defaults for untracked single-user production .env values while preserving existing local defaults.
• Ignore root ELF runtime configs and backup dumps so local secrets and restores are not committed.

Validation:

• docker compose -f docker-compose.yml config >/dev/null
• Sample production Compose environment resolves to loopback Postgres/Qdrant ports and production volume names.
• git diff --check
• cargo make fmt
• cargo make lint-fix
• cargo make checks