Improve request logging and make health check lightweight

- Log slow requests (>1s) at WARNING level with slow=true flag
- Log request timeouts at WARNING level in TimeoutMiddleware
- Replace heavy GetStatsContext with lightweight Ping in health check
- Add Ping method to database interface (SELECT 1)

internal/server/handlers.go

@@ -37,6 +37,7 @@ type HealthCheckResponse struct {
 
 // handleHealthCheck returns a handler that performs health checks.
 // Returns 200 if healthy, 503 if any check fails.
+// Uses lightweight checks to avoid timeout issues under load.
 func (s *Server) handleHealthCheck() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		ctx, cancel := context.WithTimeout(r.Context(), healthCheckTimeout)
@@ -45,13 +46,11 @@ func (s *Server) handleHealthCheck() http.HandlerFunc {
 		checks := make(map[string]string)
 		healthy := true
 
-		// Check database connectivity
-		dbStats, err := s.db.GetStatsContext(ctx)
+		// Check database connectivity with lightweight ping
+		err := s.db.Ping(ctx)
 		if err != nil {
 			checks["database"] = "error: " + err.Error()
 			healthy = false
-		} else if dbStats.ASNs == 0 && dbStats.Prefixes == 0 {
-			checks["database"] = "warning: empty database"
 		} else {
 			checks["database"] = "ok"
 		}