feat: implement order workflow, metrics, and handler unit tests

- implement UpdateOrderStatus and GetOrdersReport service methods
- implement all order, user handlers (UpdateMe, GetMyTrips, CancelOrder, GetOrder, etc.)
- extract OrderServicer interface for testability
- add Prometheus metrics middleware (requests total, duration)
- fix GetAll storage flavor for PostgreSQL ($1 placeholders)
- add 17 unit tests for order handlers via httptest
- wire Grafana datasource and update Prometheus scrape config
- update README with full API reference, pricing, roles, monitoring

internal/handler/metrics.go

@@ -0,0 +1,51 @@
+package handler
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	httpRequests = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "logiflow_http_requests_total",
+		Help: "Количество HTTP запросов",
+	}, []string{"method", "path", "status"})
+
+	httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "logiflow_http_duration_seconds",
+		Help:    "Время обработки HTTP запросов",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"method", "path"})
+)
+
+func (s *Server) MiddlewareMetrics(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+
+		wrapped := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
+		next.ServeHTTP(wrapped, r)
+
+		httpRequests.WithLabelValues(
+			r.Method,
+			r.URL.Path,
+			strconv.Itoa(wrapped.status),
+		).Inc()
+
+		httpDuration.WithLabelValues(r.Method, r.URL.Path).
+			Observe(time.Since(start).Seconds())
+	})
+}
+
+type statusRecorder struct {
+	http.ResponseWriter
+	status int
+}
+
+func (r *statusRecorder) WriteHeader(status int) {
+	r.status = status
+	r.ResponseWriter.WriteHeader(status)
+}