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

backend/config/services.yaml

@@ -167,6 +167,62 @@ services:
     App\Shared\Infrastructure\Captcha\TurnstileValidatorInterface:
         alias: App\Shared\Infrastructure\Captcha\TurnstileValidator
 
+    # =============================================================================
+    # Monitoring & Observability (Story 1.8)
+    # =============================================================================
+
+    # Prometheus CollectorRegistry - uses Redis for persistence between requests
+    Prometheus\Storage\Redis:
+        factory: ['App\Shared\Infrastructure\Monitoring\PrometheusStorageFactory', 'createRedisStorage']
+        arguments:
+            $redisUrl: '%env(REDIS_URL)%'
+
+    Prometheus\CollectorRegistry:
+        arguments:
+            $storageAdapter: '@Prometheus\Storage\Redis'
+
+    # Sentry/GlitchTip PII scrubber callback
+    App\Shared\Infrastructure\Monitoring\SentryBeforeSendCallback: ~
+
+    # Infrastructure Health Checker - shared service for health checks (DRY)
+    App\Shared\Infrastructure\Monitoring\InfrastructureHealthChecker:
+        arguments:
+            $redisUrl: '%env(REDIS_URL)%'
+
+    # Interface alias for InfrastructureHealthChecker (allows testing with stubs)
+    App\Shared\Infrastructure\Monitoring\InfrastructureHealthCheckerInterface:
+        alias: App\Shared\Infrastructure\Monitoring\InfrastructureHealthChecker
+
+    # Health Check Controller - uses shared InfrastructureHealthChecker
+    App\Shared\Infrastructure\Monitoring\HealthCheckController: ~
+
+    # Metrics Controller - restricted to internal networks in production
+    App\Shared\Infrastructure\Monitoring\MetricsController:
+        arguments:
+            $appEnv: '%kernel.environment%'
+
+    # Health Metrics Collector - exposes health_check_status gauge
+    App\Shared\Infrastructure\Monitoring\HealthMetricsCollector: ~
+
+    # Interface alias for HealthMetricsCollector (allows testing with stubs)
+    App\Shared\Infrastructure\Monitoring\HealthMetricsCollectorInterface:
+        alias: App\Shared\Infrastructure\Monitoring\HealthMetricsCollector
+
+    # Sentry context enricher - adds tenant/user/correlation_id to error reports
+    # Explicitly registered to ensure HubInterface dependency is resolved
+    App\Shared\Infrastructure\Monitoring\SentryContextEnricher:
+        arguments:
+            $sentryHub: '@Sentry\State\HubInterface'
+
+    # Monolog processors for structured logging
+    App\Shared\Infrastructure\Monitoring\CorrelationIdLogProcessor:
+        tags:
+            - { name: monolog.processor }
+
+    App\Shared\Infrastructure\Monitoring\PiiScrubberLogProcessor:
+        tags:
+            - { name: monolog.processor }
+
 # =============================================================================
 # Test environment overrides
 # =============================================================================