[TS-BACKEND] test: Add comprehensive analytics module test suite
Add unit tests for analytics module achieving 100% coverage:
- analytics.service.spec.ts: 43 tests covering all 5 public methods
- getUserMetrics: growth rate, retention rate, edge cases
- getBillingMetrics: revenue trends, subscription status, trial detection
- getUsageMetrics: action counts, peak hours, averages
- getSummary: KPIs, growth calculations
- getTrends: date truncation, empty data handling
- analytics.controller.spec.ts: 15 tests for all endpoints
- Period parameter handling (7d, 30d, 90d, 1y)
- Multi-tenant isolation validation
Part of Fase 4: Test coverage improvement (80.89% overall)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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