XY-825: [ELF prod P0] Add single-user production runbook with backup and restore proof

[yvette-carlisle]

Summary

• Expand the single-user production runbook with exact Docker Compose start, stop, health, backup, restore, Qdrant rebuild, rollback, cleanup, and provider config handling commands.
• Record a clean-volume restore/rebuild proof using local deterministic providers.
• Fix the Postgres volume mount for the PostgreSQL 18 pgvector image and route README/benchmark production-operation links to the runbook.

Validation

• docker compose -f docker-compose.yml config
• Clean-volume restore/rebuild proof: add_note succeeded, backup was non-empty, restored source row count was 1, Qdrant rebuild returned rebuilt_count 1 with zero missing/error counts, and search returned the restored note after rebuild.
• cargo make fmt
• cargo make lint-fix
• cargo make checks