feat(cache): Implement Redis Caching Layer for Listings Performance Optimization

[Emrys02]

Overview

Implement a centralized Redis caching layer for PayEasy listings using Upstash.

Important

Implementation Status: This PR establishes the core Infrastructure and Caching Wrapper logic. The API routes currently use temporary placeholder callbacks for the data source. These must be replaced with real backend logic (DB/Blockchain) in a subsequent PR.

Technical Improvements

• Redis Infrastructure: Initialized Upstash Redis in lib/redis.ts and unified listing data structures in lib/types.ts.
• Caching Logic: Implemented lib/listings.ts as an intelligent caching wrapper:
  • List Views: 15m TTL with automatic invalidation on mutations (Create/Update).
  • Detail Views: 1h TTL for static entries.
• Gateway Endpoints: Created endpoints at /api/listings and /api/listings/[id] with built-in Cache-Control headers for both server and browser-side caching.
• Configuration: Created .env.example with standard project credentials including Redis, MongoDB, JWT, and Stellar network settings.

Key Caching Details

• Key Patterns: listings:all:page:${page} and listings:detail:${id}.
• Headers: Cache-Control: public, max-age=900 (List) / max-age=3600 (Detail).

Verification

1. Set credentials in .env.local.
2. Visit /api/listings or /api/listings/1 once (Cache Miss) and twice (Cache Hit).
3. Check server logs for [Cache Hit] and [Cache Invalidation] events.

Closes #32

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