Convert Monolith to Microservices Architecture

[bit-web24]

Feature Release: Distributed Systems Architecture & URL Expiry

This merge introduces a massive architectural overhaul of the Bittuly platform, migrating the core systems to a high-performance, event-driven, distributed microservices architecture capable of handling viral scale.

🚀 Key Architectural Upgrades

1. Messaging, Resilience & Event-Driven Metrics (RabbitMQ)

• Decoupled Analytics: Link redirects no longer wait for synchronous database updates. Click tracking is now published asynchronously to RabbitMQ (click_events_queue), resulting in sub-millisecond redirection times.
• Dedicated Consumer Service: Built a brand new Rust-based consumer-service to ingest background tasks.
• Fault Tolerance: Implemented a robust "At-Least-Once" delivery system featuring Dead Letter Queues (DLQ) and mathematical exponential backoff retry mechanisms (3s -> 9s -> 27s) for failing jobs.

2. High-Concurrency & Cache Stampede Protection

• Singleflight Request Coalescing: Implemented a state-of-the-art L1 micro-cache using moka in the Rust backend. This guarantees that if a viral link generates a 200,000 req/sec spike, identical concurrent requests are coalesced in memory—ensuring the database receives exactly 1 query, completely eliminating Cache Stampedes / Thundering Herd failures.
• Gateway Scaling: Re-configured NGINX to handle up to 200,000 global concurrent connections (worker_rlimit_nofile), while maintaining strict IP-based rate limiting (20r/s per user) to protect against DDoS attacks.

3. URL Expiration Lifecycle (Phase 3)

• Precision Tracking: Added accurate microsecond expiration tracking (TIMESTAMPTZ) natively into PostgreSQL.
• Dynamic Redis Eviction: The caching layer calculates exact chronological TTLs, forcing Redis to automatically evict links from memory the exact millisecond they expire.
• Dead Link Resurrection: Developed a sophisticated Upsert model that gracefully allows users to re-shorten and reactivate exact URLs if their previous shortcode has naturally expired.

🎨 Frontend & UX Enhancements

• Seamless Error Interception: NGINX now intelligently intercepts backend 410 Gone and 404 Not Found errors, proxying them to the React Router to render the <Unavailable /> page beautifully without altering the user's URL bar.
• Modern UI Dialogs: Added explicit Confirmation Modals for safe deletion and rich "Link Details" panels.
• Expiration Controls: Integrated Date/Time pickers for precise TTL configuration on link creation, paired with visual Active/Expired UI status badges on the dashboard.