feat: Add Browser Side Performance Insights

[kylejeske]

Add @xarc/app-performance-monitor package

Client-side performance monitoring utility that automatically tracks:

• Web Vitals (LCP, FID, FCP)
• JavaScript bundle load times and sizes
• Performance timing metrics (DNS, TCP, TTFB, DOM processing)
• Runtime errors

Features:

• Zero-config auto-initialization
• SSR-safe (works in Node.js without errors)
• Framework-agnostic (React, Vue, Angular, vanilla JS)
• TypeScript support with full type definitions
• Dual builds (ESM + CJS)
• Exports metrics to console and provides API to send to analytics endpoints

Usage: import '@xarc/app-performance-monitor'; // Metrics automatically collected and available at window.performanceMetrics

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