feat: implement provider fee config, data export, load balancing, and advanced reporting

[naallahmagaji31-tech]

Summary

This PR resolves four issues from the Stellar Wave milestone by implementing new services, routes, and database migrations for each feature area.

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Changes

Issue #200 — Provider Fee Configuration

• ProviderFeeService — provider-specific fee overrides for MTN, Airtel, and Orange with full version history
• Fee versioning: each configuration gets an immutable version number; activating a new version deactivates the previous one
• Fee change approval workflow: POST /api/fees/proposals to propose, POST /api/fees/proposals/:id/review to approve or reject
• Fee simulation: POST /api/fees/simulate previews the impact of proposed parameters against a set of sample amounts before activation
• Fee analytics: GET /api/fees/analytics returns P&L-style breakdown by provider and transaction type with a daily trend
• Fee display helper: POST /api/fees/display returns a structured fee object for embedding in transaction/checkout API responses
• Migration: 20260730_create_provider_fee_configs.sql

Issue #202 — Data Export

• DataExportService — CSV, JSON, and HTML-based PDF export with streaming for large datasets
• PDF export: GET /api/exports/transactions?format=pdf — produces a printable HTML document (renderable by headless browser)
• Scheduled exports: POST /api/exports/scheduled — daily, weekly, or monthly jobs with email delivery flag
• Export templates: GET /api/exports/templates — built-in templates (monthly summary, failed transactions, PDF history, GDPR package)
• GDPR-compliant data export: GET /api/exports/gdpr — full user data package (transactions, profile, KYC, audit logs) as a downloadable JSON file
• Export access logging for full audit trail
• Migration: 20260730_create_data_exports.sql

Issue #203 — Provider Load Balancing

• ProviderLoadBalancer service — pluggable routing strategies across MTN, Airtel, and Orange
• Strategies: round_robin (default), least_connections, weighted, random
• Health-aware routing: degraded/unhealthy providers are automatically skipped
• Capacity tracking: per-provider maxConcurrentRequests, weight, and isEnabled flags
• Sticky sessions: Redis-backed with configurable TTL (default 5 minutes)
• Per-provider metrics: request counts, failure counts, average response time
• Admin API for dynamic config changes (PUT /api/providers/load-balancer/config) and manual health overrides (POST /api/providers/load-balancer/health/:name)
• Migration: 20260730_create_provider_load_balancer.sql

Issue #205 — Advanced Reporting

• AdvancedReportingService — typed report generation engine with Redis caching
• P&L report: GET /api/reports/pnl — revenue, volume, effective fee rate, daily breakdown
• Settlement report: GET /api/reports/settlement — per-provider settled/pending/failed amounts with settlement rate
• KYC compliance report: GET /api/reports/kyc-compliance — approval rates by verification level with daily submission trend
• Custom report builder: POST /api/reports/custom — specify metrics (count, sum_amount, sum_fees, avg_amount), groupBy fields, and filters; returns JSON or CSV
• Scheduled report generation: POST /api/reports/scheduled — daily/weekly/monthly with email distribution and recipient list
• Report archival: POST /api/reports/archive with configurable retention; GET /api/reports/archive for retrieval
• Migration: 20260730_create_advanced_reports.sql

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Closes #200
Closes #202
Closes #203
Closes #205