docs: add testing, development, and monitoring documentation

- Create 13-testing-development.md with:
  - Testing pyramid strategy (unit, integration, E2E)
  - Local development setup with Docker Compose
  - Database migration procedures
  - Feature flag system design
  - Accessibility (WCAG 2.1) requirements
  - CI/CD pipeline configuration

- Create 14-monitoring-observability.md with:
  - Three pillars: metrics, logs, traces
  - SLI/SLO monitoring and error budgets
  - Structured logging format
  - Sentry error tracking
  - Distributed tracing
  - Alert hierarchy and dashboards

- Update REVIEW_PROGRESS.md with iteration 3 changes
- Export 21 new diagram images
- Total: 15 docs, 191 diagrams

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MuhsinunC

docs/architecture/12-reliability-scalability.md

@@ -708,4 +708,5 @@ flowchart TD
 ---
 
 **Previous:** [11-operational-runbooks.md](./11-operational-runbooks.md) - Operational Runbooks
+**Next:** [13-testing-development.md](./13-testing-development.md) - Testing & Development
 **Index:** [00-overview.md](./00-overview.md) - System Overview