feat: enable redis aof persistence

[GitAddRemote]

Closes #126

Summary

• enable Redis AOF persistence with appendfsync everysec in both production and staging compose stacks and rename the Redis volumes accordingly
• verify the labeled pre-deploy PostgreSQL backup exists in B2 before production deploy continues
• document Redis persistence and recovery in infra/docs/redis.md, plus update CI/CD and infra tests to match the new deploy contract

Testing

• git -C /tmp/station-issue-126 diff --check
• node /tmp/station-issue-126/infra/tests/infrastructure.test.mjs

Notes

• #126 is now In Progress on the Station Kanban Board
• backup-db.sh now prefers BACKUP_LABEL over the positional label argument so the release workflow can stamp pre-deploy snapshots consistently
• no new GitHub environment secrets are required for this ticket beyond the B2 secrets already introduced in #125