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/tests/Unit/Shared/Infrastructure/Monitoring/MetricsCollectorTest.php

@@ -0,0 +1,199 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Shared\Infrastructure\Monitoring;
+
+use App\Shared\Infrastructure\Monitoring\MetricsCollector;
+use App\Shared\Infrastructure\Tenant\TenantConfig;
+use App\Shared\Infrastructure\Tenant\TenantContext;
+use App\Shared\Infrastructure\Tenant\TenantId;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Prometheus\CollectorRegistry;
+use Prometheus\Counter;
+use Prometheus\Histogram;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Event\RequestEvent;
+use Symfony\Component\HttpKernel\Event\TerminateEvent;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+
+/**
+ * @see Story 1.8 - T3.4: Custom metrics (requests_total, request_duration_seconds)
+ */
+#[CoversClass(MetricsCollector::class)]
+final class MetricsCollectorTest extends TestCase
+{
+    private CollectorRegistry $registry;
+    private TenantContext $tenantContext;
+    private MetricsCollector $collector;
+    private Counter $requestsCounter;
+    private Histogram $durationHistogram;
+    private Counter $loginFailuresCounter;
+
+    protected function setUp(): void
+    {
+        $this->requestsCounter = $this->createMock(Counter::class);
+        $this->durationHistogram = $this->createMock(Histogram::class);
+        $this->loginFailuresCounter = $this->createMock(Counter::class);
+
+        $this->registry = $this->createMock(CollectorRegistry::class);
+        $this->registry->method('getOrRegisterCounter')
+            ->willReturnCallback(fn (string $ns, string $name) => match ($name) {
+                'http_requests_total' => $this->requestsCounter,
+                'login_failures_total' => $this->loginFailuresCounter,
+                default => $this->createMock(Counter::class),
+            });
+        $this->registry->method('getOrRegisterHistogram')
+            ->willReturn($this->durationHistogram);
+
+        $this->tenantContext = new TenantContext();
+        $this->collector = new MetricsCollector($this->registry, $this->tenantContext);
+    }
+
+    protected function tearDown(): void
+    {
+        $this->tenantContext->clear();
+    }
+
+    #[Test]
+    public function itRecordsRequestMetricsWithoutTenant(): void
+    {
+        $request = Request::create('/api/users', 'GET');
+        $request->attributes->set('_route', 'get_users');
+        $response = new Response('', 200);
+
+        $kernel = $this->createMock(HttpKernelInterface::class);
+
+        // Simulate request start
+        $requestEvent = new RequestEvent($kernel, $request, HttpKernelInterface::MAIN_REQUEST);
+        $this->collector->onKernelRequest($requestEvent);
+
+        // Expect metrics to be recorded with tenant_id="none"
+        $this->requestsCounter->expects(self::once())
+            ->method('inc')
+            ->with(['GET', 'get_users', '200', 'none']);
+
+        $this->durationHistogram->expects(self::once())
+            ->method('observe')
+            ->with(
+                self::greaterThan(0),
+                ['GET', 'get_users', 'none'],
+            );
+
+        // Simulate request end
+        $terminateEvent = new TerminateEvent($kernel, $request, $response);
+        $this->collector->onKernelTerminate($terminateEvent);
+    }
+
+    #[Test]
+    public function itRecordsRequestMetricsWithTenant(): void
+    {
+        $tenantConfig = new TenantConfig(
+            tenantId: TenantId::fromString('a1b2c3d4-e5f6-7890-abcd-ef1234567890'),
+            subdomain: 'ecole-alpha',
+            databaseUrl: 'postgresql://test@localhost/test',
+        );
+        $this->tenantContext->setCurrentTenant($tenantConfig);
+
+        $request = Request::create('/api/users', 'POST');
+        $request->attributes->set('_route', 'create_user');
+        $response = new Response('', 201);
+
+        $kernel = $this->createMock(HttpKernelInterface::class);
+
+        $requestEvent = new RequestEvent($kernel, $request, HttpKernelInterface::MAIN_REQUEST);
+        $this->collector->onKernelRequest($requestEvent);
+
+        $this->requestsCounter->expects(self::once())
+            ->method('inc')
+            ->with(['POST', 'create_user', '201', 'ecole-alpha']);
+
+        $terminateEvent = new TerminateEvent($kernel, $request, $response);
+        $this->collector->onKernelTerminate($terminateEvent);
+    }
+
+    #[Test]
+    public function itSkipsMetricsEndpoint(): void
+    {
+        $request = Request::create('/metrics', 'GET');
+        $request->attributes->set('_route', 'prometheus_metrics');
+        $response = new Response('', 200);
+
+        $kernel = $this->createMock(HttpKernelInterface::class);
+
+        $requestEvent = new RequestEvent($kernel, $request, HttpKernelInterface::MAIN_REQUEST);
+        $this->collector->onKernelRequest($requestEvent);
+
+        // Should NOT record metrics for /metrics endpoint
+        $this->requestsCounter->expects(self::never())->method('inc');
+        $this->durationHistogram->expects(self::never())->method('observe');
+
+        $terminateEvent = new TerminateEvent($kernel, $request, $response);
+        $this->collector->onKernelTerminate($terminateEvent);
+    }
+
+    #[Test]
+    public function itSkipsHealthEndpoint(): void
+    {
+        $request = Request::create('/health', 'GET');
+        $request->attributes->set('_route', 'health_check');
+        $response = new Response('', 200);
+
+        $kernel = $this->createMock(HttpKernelInterface::class);
+
+        $requestEvent = new RequestEvent($kernel, $request, HttpKernelInterface::MAIN_REQUEST);
+        $this->collector->onKernelRequest($requestEvent);
+
+        $this->requestsCounter->expects(self::never())->method('inc');
+
+        $terminateEvent = new TerminateEvent($kernel, $request, $response);
+        $this->collector->onKernelTerminate($terminateEvent);
+    }
+
+    #[Test]
+    public function itRecordsLoginFailureWithoutTenant(): void
+    {
+        $this->loginFailuresCounter->expects(self::once())
+            ->method('inc')
+            ->with(['none', 'invalid_credentials']);
+
+        $this->collector->recordLoginFailure();
+    }
+
+    #[Test]
+    public function itRecordsLoginFailureWithTenant(): void
+    {
+        $tenantConfig = new TenantConfig(
+            tenantId: TenantId::fromString('a1b2c3d4-e5f6-7890-abcd-ef1234567890'),
+            subdomain: 'ecole-beta',
+            databaseUrl: 'postgresql://test@localhost/test',
+        );
+        $this->tenantContext->setCurrentTenant($tenantConfig);
+
+        $this->loginFailuresCounter->expects(self::once())
+            ->method('inc')
+            ->with(['ecole-beta', 'rate_limited']);
+
+        $this->collector->recordLoginFailure('rate_limited');
+    }
+
+    #[Test]
+    public function itIgnoresSubrequests(): void
+    {
+        $request = Request::create('/api/test', 'GET');
+        $kernel = $this->createMock(HttpKernelInterface::class);
+
+        // Subrequest should be ignored
+        $requestEvent = new RequestEvent($kernel, $request, HttpKernelInterface::SUB_REQUEST);
+        $this->collector->onKernelRequest($requestEvent);
+
+        $this->requestsCounter->expects(self::never())->method('inc');
+
+        $response = new Response('', 200);
+        $terminateEvent = new TerminateEvent($kernel, $request, $response);
+        $this->collector->onKernelTerminate($terminateEvent);
+    }
+}