feat(M48): continuous TLS health monitoring — endpoint state machine, shared tlsprobe, 8 API endpoints, GUI

Adds continuous TLS endpoint health monitoring that closes the deploy→verify→monitor loop.
After M25 verifies a deployment succeeded once, M48 continuously confirms it stays healthy.

Key components:
- Shared `internal/tlsprobe/` package extracted from network scanner for reuse
- Health status state machine: healthy → degraded (2 failures) → down (5 failures),
  plus cert_mismatch when served fingerprint differs from expected
- 8th scheduler loop (60s tick, per-endpoint configurable intervals)
- PostgreSQL migration 000011: endpoint_health_checks + endpoint_health_history tables
- 8 REST API endpoints (CRUD, history, acknowledge, summary)
- Health Monitor GUI page with summary bar, status table, create modal, auto-refresh
- 38 new tests (5 tlsprobe + 11 domain + 10 service + 8 handler + 4 frontend)
- All coverage thresholds maintained (service 68%, handler 83%, domain 87%, middleware 63%)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/server/main.go

@@ -259,6 +259,29 @@ func main() {
 		}
 	}
 
+	// Initialize health check service (M48)
+	var healthCheckService *service.HealthCheckService
+	var healthCheckHandler *handler.HealthCheckHandler
+	if cfg.HealthCheck.Enabled {
+		healthCheckRepo := postgres.NewHealthCheckRepository(db)
+		healthCheckService = service.NewHealthCheckService(
+			healthCheckRepo,
+			auditService,
+			logger,
+			cfg.HealthCheck.MaxConcurrent,
+			time.Duration(cfg.HealthCheck.DefaultTimeout)*time.Millisecond,
+			cfg.HealthCheck.HistoryRetention,
+			cfg.HealthCheck.AutoCreate,
+		)
+		healthCheckHandler = handler.NewHealthCheckHandler(healthCheckService)
+		logger.Info("health check service enabled",
+			"interval", cfg.HealthCheck.CheckInterval.String(),
+			"max_concurrent", cfg.HealthCheck.MaxConcurrent)
+	} else {
+		// Create a no-op health check handler for route registration
+		healthCheckHandler = handler.NewHealthCheckHandler(nil)
+	}
+
 	logger.Info("initialized all handlers")
 
 	// Create context with cancellation
@@ -289,6 +312,11 @@ func main() {
 		sched.SetDigestInterval(cfg.Digest.Interval)
 		logger.Info("digest scheduler enabled", "interval", cfg.Digest.Interval.String())
 	}
+	if healthCheckService != nil {
+		sched.SetHealthCheckService(healthCheckService)
+		sched.SetHealthCheckInterval(cfg.HealthCheck.CheckInterval)
+		logger.Info("health check scheduler enabled", "interval", cfg.HealthCheck.CheckInterval.String())
+	}
 
 	// Start scheduler
 	logger.Info("starting scheduler")
@@ -319,6 +347,7 @@ func main() {
 		Verification:  verificationHandler,
 		Export:        exportHandler,
 		Digest:        *digestHandler,
+		HealthChecks:  healthCheckHandler,
 	})
 	// Register EST (RFC 7030) handlers if enabled
 	if cfg.EST.Enabled {