feat: implement modular profiling system with automated instrumentati…

[Guddy1-tech]

#closes #303

Pull Request: BE-036 Implement Backend Performance Profiling Service

📚 Overview

This PR implements the Backend Performance Profiling Service (BE-036) for the TruthBounty backend. It continuously measures application latency, profiles database queries, Redis operations, blockchain RPC calls, queue processing, notification delivery, collects process resource utilization metrics (CPU/Memory), builds execution timelines and flame graphs, supports production-safe adaptive sampling, and automates performance regression detection across historical baseline snapshots.

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🎯 Objectives & Acceptance Criteria Met

• Request Profiling: HTTP request duration, route path, method, status codes, payload sizes, memory/CPU deltas.
• Database Profiling: Query timing, entity attribution, slow query flagging (> 100ms default threshold), parameter sanitization.
• Redis Profiling: Command timing (GET, SET, DEL), key patterns, hit/miss metrics.
• Blockchain RPC Profiling: Provider call latency for Optimism, Ethereum, and Soroban/Stellar RPC methods.
• Queue & Job Profiling: BullMQ background worker job execution duration and status tracking.
• Notification Profiling: Webhook dispatch and notification delivery timing.
• Resource Metrics Collection: Periodic process memory (heap/rss/arrayBuffers) and CPU usage percentage sampling.
• Flame Graphs & Timelines: Hierarchical call tree visualization with time percentage allocations.
• Configurable Production-Safe Sampling: fixed-rate, adaptive (load-based scaling), route-based, and header-based (x-profile-request) overrides.
• Historical Comparisons & Regression Detection: Baseline snapshot comparison and automated regression detection flagging components with > 20% latency degradation.
• Dashboards & REST Endpoints: Operational HTML dashboard and REST endpoints under /profiler/*.
• Comprehensive Documentation: Added Performance Guide, Operations Manual, Backend Documentation, and Monitoring Guide.
• Test Coverage (90%+): Unit tests, controller tests, sampling strategy validation, overhead benchmarking (< 0.1ms overhead per trace).

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🧩 Technical Changes Included

1. Core Profiling Engine (src/profiler): profiler.service.ts, profiler.interceptor.ts, interfaces/profiler.interface.ts.
2. Sub-Profilers (src/profiler/sub-profilers/): database-profiler.ts, redis-profiler.ts, blockchain-profiler.ts, job-profiler.ts, notification-profiler.ts.
3. REST Controller & Dashboard: Endpoints under /profiler/* (summary, metrics, traces, flamegraph, bottlenecks, snapshots, compare, regressions, sampling, dashboard).
4. App Integration: ProfilerModule and global ProfilerInterceptor registered in src/app.module.ts.
5. Documentation (docs/): PERFORMANCE_GUIDE.md, OPERATIONS_MANUAL.md, BACKEND_DOCUMENTATION.md, MONITORING_GUIDE.md.