feat: add redis session management for horizontal scaling in k8s

[harsharahul]

Kubernetes Multi-Pod Scaling for Memos

Description

This update enables Memos to scale horizontally across multiple Kubernetes pods by implementing distributed session management with Redis. Previously, SSO authentication would fail when page redirects hit different pods due to per-pod session storage. Now sessions are shared across all pods, enabling true HA deployment.

Features

• Distributed Session Management: Redis-backed cache with local fallback
• Multi-Pod SSO Support: Fixes authentication failures across pod redirects
• Backward compatible:
• Existing deployments work unchanged
• Redis not configured defaults to local cache which is the existing behaviour

🔄 Migration Path

Existing Deployments

• ✅ No Changes Required: Existing single-pod deployments work unchanged
• ✅ Opt-in Scaling: Add Redis URL to enable multi-pod features
• ✅ Backward Compatible: All existing APIs and behavior preserved