Add Litestream backup sidecar to existing StatefulSet

[vcarl]

Context

Part of load balancer architecture work (see PR #228 for full analysis).

Risk: Low | Reward: High | Code Changes: None

Description

Add Litestream sidecar to the existing StatefulSet for continuous SQLite backup to DigitalOcean Spaces.

Why This is Safe

• Read-only operation on SQLite (uses WAL mode)
• Doesn't affect app behavior
• Provides disaster recovery immediately
• Easiest rollback: just remove the sidecar

Tasks

• Create DigitalOcean Spaces bucket for backups
• Add Litestream credentials to modbot-env secret:
  • LITESTREAM_ACCESS_KEY_ID
  • LITESTREAM_SECRET_ACCESS_KEY
• Create cluster/litestream-config.yaml ConfigMap with DO Spaces endpoint
• Add Litestream sidecar container to cluster/deployment.yaml
• Test backup/restore in staging

References

• Litestream docs
• PR Architecture analysis: Load balancing with SQLite constraint #228 (architecture analysis)
• /notes/LOAD_BALANCER_QUICK_REF.md