feat: Observabilité et monitoring complet

Implémentation complète de la stack d'observabilité pour le monitoring
de la plateforme multi-tenant Classeo.

## Error Tracking (GlitchTip)
- Intégration Sentry SDK avec GlitchTip auto-hébergé
- Scrubber PII avant envoi (RGPD: emails, tokens JWT, NIR français)
- Contexte enrichi: tenant_id, user_id, correlation_id
- Configuration backend (sentry.yaml) et frontend (sentry.ts)

## Metrics (Prometheus)
- Endpoint /metrics avec restriction IP en production
- Métriques HTTP: requests_total, request_duration_seconds (histogramme)
- Métriques sécurité: login_failures_total par tenant
- Métriques santé: health_check_status (postgres, redis, rabbitmq)
- Storage Redis pour persistance entre requêtes

## Logs (Loki)
- Processors Monolog: CorrelationIdLogProcessor, PiiScrubberLogProcessor
- Détection PII: emails, téléphones FR, tokens JWT, NIR français
- Labels structurés: tenant_id, correlation_id, level

## Dashboards (Grafana)
- Dashboard principal: latence P50/P95/P99, error rate, RPS
- Dashboard par tenant: métriques isolées par sous-domaine
- Dashboard infrastructure: santé postgres/redis/rabbitmq
- Datasources avec UIDs fixes pour portabilité

## Alertes (Alertmanager)
- HighApiLatencyP95/P99: SLA monitoring (200ms/500ms)
- HighErrorRate: error rate > 1% pendant 2 min
- ExcessiveLoginFailures: détection brute force
- ApplicationUnhealthy: health check failures

## Infrastructure
- InfrastructureHealthChecker: service partagé (DRY)
- HealthCheckController: endpoint /health pour load balancers
- Pre-push hook: make ci && make e2e avant push

monitoring/prometheus/prometheus.yml

@@ -0,0 +1,52 @@
+# Prometheus Configuration for Classeo
+# Scrapes metrics from PHP backend and other services
+
+global:
+  scrape_interval: 15s
+  evaluation_interval: 15s
+  external_labels:
+    environment: ${ENVIRONMENT:-development}
+    project: classeo
+
+# Alerting configuration
+alerting:
+  alertmanagers:
+    - static_configs:
+        - targets:
+            - alertmanager:9093
+
+# Load alert rules
+rule_files:
+  - /etc/prometheus/alerts.yml
+
+# Scrape configurations
+scrape_configs:
+  # Prometheus self-monitoring
+  - job_name: 'prometheus'
+    static_configs:
+      - targets: ['localhost:9090']
+
+  # PHP Backend metrics
+  - job_name: 'classeo-backend'
+    metrics_path: '/metrics'
+    static_configs:
+      - targets: ['php:8000']
+    relabel_configs:
+      - source_labels: [__address__]
+        target_label: instance
+        replacement: 'classeo-backend'
+
+  # Redis metrics (via redis_exporter would be added in production)
+  # For now, we rely on application-level metrics
+
+  # PostgreSQL metrics (via postgres_exporter would be added in production)
+  # For now, we rely on application-level metrics
+
+  # RabbitMQ metrics
+  - job_name: 'rabbitmq'
+    static_configs:
+      - targets: ['rabbitmq:15692']
+    relabel_configs:
+      - source_labels: [__address__]
+        target_label: instance
+        replacement: 'classeo-rabbitmq'