[BE-88] Redis caching for hot read paths

[yusuftomilola]

Overview

@nestjs/cache-manager, cache-manager-ioredis, and ioredis are all dependencies, and Redis is already required for Bull — but caching is not applied to the read paths that would benefit most.

Tasks

• Configure the cache module with a Redis store and sensible default TTL.
• Cache: public workspace listings, membership plan listings, hub settings, and dashboard aggregates.
• Add explicit invalidation on write — updating a plan or workspace must purge its cached entries immediately.
• Namespace cache keys per entity and include a version prefix so a deploy can invalidate wholesale.
• Never cache authenticated, user-specific responses under a shared key.

Acceptance Criteria

• Repeated public plan/workspace reads hit Redis, not Postgres (demonstrated by query counts or logs).
• Editing a plan is reflected on the next public read with no stale window.
• A test proves user A never receives user B's cached data.

Notes for Contributors

Comment below to be assigned.

[odiliflash-ops]

I would love to fix this issue