feat: external API improvements - circuit breaker, timeout, brotli compression, image optimization, PgBouncer pooling

[DeborahOlaboye]

Issue #382 - Add database connection pooling with PgBouncer integration

• RDS Proxy (PgBouncer transaction mode) configured in infrastructure
• Connection pool size tuned per environment with env vars
• Prepared statement registry with automatic deallocation on overflow
• Graceful pool exhaustion handling with exponential backoff
• Pool metrics monitoring (active, idle, waiting, peak)
• Connection leak detection and prevention with lease manager

Issue #383 - Implement API response compression with brotli

• Brotli compression at level 5 with gzip fallback for older clients
• Configurable compression level per endpoint
• Minimum size threshold of 1KB before compression
• Cache-friendly Content-Encoding and X-Compression headers
• Graceful degradation if compression does not reduce size

Issue #384 - Optimize frontend image loading with responsive sizes and WebP

• Enhanced OptimizedImage component with responsive sizes attribute
• Device sizes and image sizes configured in next.config.ts
• WebP/AVIF format with JPEG fallback (via next/image)
• Blur-up placeholder generation for smooth loading
• Lazy loading below-the-fold images, priority loading for above
• CSP-compatible image CDN remote patterns

Issue #398 - Add timeout and circuit breaker for external API calls

• Configurable timeout per external service (Stellar, Stripe)
• Circuit breaker with failure threshold and recovery timeout
• Fallback responses for degraded functionality
• Timeout and circuit breaker metrics tracking
• Graceful degradation when circuit is open
• Manual circuit reset for emergency recovery via API endpoint

Closes #382
Closes #383
Closes #384
Closes #398

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