Add Redis caching for session endpoints to improve performance

## Problem Statement

- Currently, every time the user refreshes their dashboard or checks session history, the backend fetches data directly from MongoDB.
- This increases response time and database load, especially when users frequently start, pause, or complete sessions.

## Proposed Solution

- Add a Redis caching layer to temporarily store frequently accessed session data (/current, /history) for faster retrieval.

## Implementation idea:

- Use ioredis or redis npm package.

- Cache key format: session:${userEmail}

- Set a TTL of 5–10 minutes.

- Invalidate cache whenever session data is created, updated, or deleted.

## Alternatives Considered

- Using in-memory caching (e.g., node-cache) — but it wouldn’t scale across multiple backend instances.

- MongoDB indexing — helps query speed but doesn’t reduce repeated hits.

## Additional Context

- This would improve user experience on dashboards and analytics pages, reducing API response times by 30–50% while easing database loa

Start by locating the backend handlers for /current and /history, the MongoDB session access, and the create, update, and delete paths. Check the existing package setup before choosing ioredis or redis. Done means the endpoints use the specified session cache with a 5–10 minute TTL and cache entries are invalidated whenever session data changes.

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