docs: verify database restore disaster recovery procedure

[tun1r]

Closes #442

Summary

• Adds a database restore disaster recovery runbook for the SQLite-backed backend.
• Adds npm run db:restore:verify to create a backup, restore it into an isolated probe database, run PRAGMA quick_check, and compare table/row counts.
• Documents local and Docker Compose backup/restore steps, rollback handling, post-restore QA checks, and PR evidence format.
• Links the restore verification workflow from the backend README and scripts README.

Verification

Passed for this change:

• node --check scripts/verify-db-restore.js
• npm run db:restore:verify -- --source ./prisma/dev.db --backup-dir /tmp/anchorpoint-dr-442-verify

Restore verification result:

• Tables verified: 7
• Rows verified: 2

Existing repo/tooling failures observed

I also checked the broader backend commands and found failures that appear unrelated to this PR because they occur outside the files touched here:

• npm run build -w backend fails on pre-existing TypeScript/tsconfig syntax errors, including backend/tsconfig.json, src/api/controllers/auth.controller.ts, src/services/auth.service.ts, and src/services/webhook.service.ts.
• npm run lint -w backend fails in this fresh clone because eslint is not installed locally.
• npm test -w backend is likewise blocked by missing local test tooling in this fresh clone.

This PR keeps scope to the #442 disaster recovery verification task and does not modify the unrelated broken TypeScript or project tooling files.

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