feat(analytics): implementar Advanced Analytics - TASK-027

Implementacion completa de analytics avanzadas:

Trend Analysis (TrendAnalyzer):
- analyze_deployment_frequency_trend(days=90)
  * Weekly aggregation
  * Trend direction: improving/declining/stable
  * Average weekly change
  * Week-over-week comparison
  * Statistics: mean, median, std_dev, min, max

- analyze_lead_time_trend(days=90)
  * Weekly average lead times
  * Inverse trend calculation (lower is better)
  * Statistical summary

Comparative Analytics (ComparativeAnalytics):
- period_over_period_comparison()
  * Compare current vs previous period
  * Deployment frequency comparison
  * Lead time comparison
  * Change failure rate comparison
  * Percent change calculations
  * Automated summary generation

Historical Reporting (HistoricalReporting):
- generate_monthly_report(months=6)
  * Monthly aggregation
  * Deployment frequency per month
  * Average lead time per month
  * Best/worst month identification
  * Summary statistics

Anomaly Detection (AnomalyTrendDetector):
- detect_duration_anomalies(days=30)
  * IQR method (Q1, Q3, IQR)
  * Lower/upper bounds calculation
  * Anomaly classification: unusually_fast/unusually_slow
  * Anomaly rate tracking
  * Top 20 recent anomalies

Performance Forecasting (PerformanceForecasting):
- forecast_next_month(historical_months=6)
  * Linear extrapolation
  * Deployment frequency prediction
  * Lead time prediction
  * Trend direction
  * Confidence levels (low/medium)

API Endpoints:
- GET /api/dora/analytics/trends/deployment-frequency/
- GET /api/dora/analytics/trends/lead-time/
- GET /api/dora/analytics/comparative/period-over-period/
- GET /api/dora/analytics/historical/monthly/
- GET /api/dora/analytics/anomalies/
- GET /api/dora/analytics/forecast/

Algorithms:
- Linear regression for trend calculation
- IQR method for anomaly detection
- Simple linear forecast
- Statistical analysis (mean, median, stdev)

Features:
- Trend direction detection (>5% significance)
- Automated summaries
- Configurable time periods
- Rate limiting applied
- Comprehensive statistics

Archivos:
- dora_metrics/advanced_analytics.py (nuevo)
- dora_metrics/views.py (actualizado)
- dora_metrics/urls.py (actualizado)
- docs/analytics/TASK-027-advanced-analytics.md

Story Points: 8 SP
Estado: COMPLETADO

Author: claude