#591 Implement infrastructure as code (IaC) with Terraform

[Purity-Euphemia]

Closes #591

Summary

Add compatibility support for local analytics and cost tracking validation, plus Prometheus scrape alias support.

Changes

• src/analytics/analytics.controller.ts
  • Added POST /analytics/event compatibility endpoint.
• src/monitoring/cost.controller.ts
  • Added POST /metrics/cost to record hourly infrastructure cost.
  • Added GET /monitoring/cost/summary for 24h cost summary.
• src/monitoring/dto/record-cost.dto.ts
  • Added validated DTO for cost payloads.
• src/monitoring/monitoring.module.ts
  • Registered CostController, CostTrackingService, and CostSchedulerService.
• src/monitoring/metrics/prometheus.controller.ts
  • Added legacy alias GET /observability/metrics/export/prometheus for compatibility.
• src/observability/README.md
  • Updated docs to show /metrics as the main Prometheus scrape endpoint and alias support.

Tests

• src/monitoring/cost.controller.spec.ts
  • Verifies hourly cost recording and summary response.
• src/monitoring/metrics/prometheus.controller.spec.ts
  • Verifies both /metrics and /observability/metrics/export/prometheus alias behavior.

Notes

• Existing analytics event tracking via POST /analytics/events remains unchanged.
• The new /analytics/event endpoint provides backward-compatible support for legacy tooling expecting a single-event route.
• Prometheus metrics are still exposed on /metrics, with an additional compatibility alias.

Validation

1. Run unit tests covering the new controllers.
2. Send a POST request to /metrics/cost with { "amountUsd": 5 } and verify success.
3. Send a GET request to /metrics and /observability/metrics/export/prometheus and verify Prometheus text format.
4. Send a POST request to /analytics/event with category and action and verify event tracking is accepted.

[RUKAYAT-CODER]

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