feat: implement Redis-based caching layer for service discovery (#316)

[Abhushan187]

Closes #316

Changes by file

File	Change
server/package.json	Added ioredis ^5.6.1 dependency.
server/config/redis.js	New. Redis connection, getOrSetCache helper (cache-aside with TTL), deleteCachePattern for wildcard invalidation, graceful disconnect.
server/controllers/issueController.js	Wrapped getNearbyIssues with getOrSetCache (5-min TTL). Added cache invalidation in createIssue and updateIssueStatus for the affected category.
server/server.js	Imported disconnectRedis; added SIGTERM/SIGINT graceful shutdown handler.
.env.example / server/.env.example	Added REDIS_URL documentation.

Technical Notes

• ioredis chosen over node-redis for built-in cluster support, pipelining, and robust reconnection.
• Cache key format: nearby:{lat}:{lng}:{category}:{radius}:{zoom} — lat/lng rounded to 4 decimals (~11m precision) to balance granularity vs cache hit rate.
• getOrSetCache falls back to DB query on any Redis error — no cache outage takes down the API.
• deleteCachePattern uses scanStream + pipeline to avoid KEYS blocking on large datasets.
• TTL is 300 seconds (5 minutes) as requested. Cache invalidation is fire-and-forget (.catch on promise) to avoid blocking the response.
• Graceful shutdown ensures Redis connection is closed before process exit, preventing connection leaks in containerized environments.

[vercel]

@Abhushan187 is attempting to deploy a commit to the souma9830's projects Team on Vercel.

A member of the Team first needs to authorize it.

[souma9830]

Resolve conflict and tell me under which open source program
you are ?

[Abhushan187]

Resolve conflict and tell me under which open source program you are ?

merge conflict resolved and im nsoc'26 contributor ,is this project part of gssoc'26 as well btw ?

[souma9830]

still have merge conflict

[Abhushan187]

still have merge conflict

checkout now and please merge it before 15th june for nsoc evaluation