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

frontend/src/lib/monitoring/webVitals.ts

@@ -0,0 +1,115 @@
+/**
+ * Web Vitals monitoring for frontend performance.
+ *
+ * Captures Core Web Vitals (LCP, FID, CLS) and sends to analytics.
+ * These metrics are critical for user experience and SEO.
+ *
+ * @see Story 1.8 - T8.4: Web Vitals (FCP, LCP, TTI)
+ */
+
+import { onCLS, onFCP, onINP, onLCP, onTTFB, type Metric } from 'web-vitals';
+
+type VitalsReporter = (metric: VitalMetric) => void;
+
+export interface VitalMetric {
+	name: 'CLS' | 'FCP' | 'INP' | 'LCP' | 'TTFB';
+	value: number;
+	rating: 'good' | 'needs-improvement' | 'poor';
+	delta: number;
+	id: string;
+}
+
+/**
+ * Web Vitals thresholds (Core Web Vitals 2024 standards).
+ *
+ * - LCP (Largest Contentful Paint): < 2.5s good, < 4s needs improvement
+ * - FCP (First Contentful Paint): < 1.8s good, < 3s needs improvement
+ * - INP (Interaction to Next Paint): < 200ms good, < 500ms needs improvement
+ * - CLS (Cumulative Layout Shift): < 0.1 good, < 0.25 needs improvement
+ * - TTFB (Time to First Byte): < 800ms good, < 1.8s needs improvement
+ */
+const THRESHOLDS = {
+	LCP: { good: 2500, needsImprovement: 4000 },
+	FCP: { good: 1800, needsImprovement: 3000 },
+	INP: { good: 200, needsImprovement: 500 },
+	CLS: { good: 0.1, needsImprovement: 0.25 },
+	TTFB: { good: 800, needsImprovement: 1800 }
+} as const;
+
+function getRating(
+	name: VitalMetric['name'],
+	value: number
+): 'good' | 'needs-improvement' | 'poor' {
+	const threshold = THRESHOLDS[name];
+	if (value <= threshold.good) return 'good';
+	if (value <= threshold.needsImprovement) return 'needs-improvement';
+	return 'poor';
+}
+
+function createVitalMetric(metric: Metric): VitalMetric {
+	return {
+		name: metric.name as VitalMetric['name'],
+		value: metric.value,
+		rating: getRating(metric.name as VitalMetric['name'], metric.value),
+		delta: metric.delta,
+		id: metric.id
+	};
+}
+
+/**
+ * Initialize Web Vitals collection.
+ *
+ * @param reporter - Callback function to report metrics (e.g., to analytics)
+ */
+export function initWebVitals(reporter: VitalsReporter): void {
+	// Core Web Vitals
+	onLCP((metric) => reporter(createVitalMetric(metric)));
+	onCLS((metric) => reporter(createVitalMetric(metric)));
+	onINP((metric) => reporter(createVitalMetric(metric)));
+
+	// Other Web Vitals
+	onFCP((metric) => reporter(createVitalMetric(metric)));
+	onTTFB((metric) => reporter(createVitalMetric(metric)));
+}
+
+/**
+ * Default reporter that logs to console (dev) or sends to backend (prod).
+ */
+export function createDefaultReporter(options: {
+	endpoint?: string;
+	debug?: boolean;
+}): VitalsReporter {
+	return (metric: VitalMetric) => {
+		// Log in development
+		if (options.debug) {
+			console.log(`[WebVitals] ${metric.name}: ${metric.value.toFixed(2)} (${metric.rating})`);
+		}
+
+		// Send to analytics endpoint in production
+		if (options.endpoint) {
+			// Use sendBeacon for reliability during page unload
+			const body = JSON.stringify({
+				metric: metric.name,
+				value: metric.value,
+				rating: metric.rating,
+				delta: metric.delta,
+				id: metric.id,
+				timestamp: Date.now(),
+				url: window.location.href
+			});
+
+			if (navigator.sendBeacon) {
+				navigator.sendBeacon(options.endpoint, body);
+			} else {
+				fetch(options.endpoint, {
+					method: 'POST',
+					body,
+					headers: { 'Content-Type': 'application/json' },
+					keepalive: true
+				}).catch(() => {
+					// Silently fail - vitals are best-effort
+				});
+			}
+		}
+	};
+}