feat(api): add log webhook notification service

Implement webhook notifications for log error threshold alerts with
configurable thresholds, time windows, and cooldown periods.

- Add LogWebhookService with Redis-backed configuration storage
- Add admin endpoints for webhook config management (GET/PUT)
- Trigger webhook notifications when error count exceeds threshold
- Support status code threshold and error message detection
- Include sample log record data in webhook payload

internal/service/log_webhook_test.go

@@ -0,0 +1,60 @@
+package service
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"sync/atomic"
+	"testing"
+
+	"github.com/alicebob/miniredis/v2"
+	"github.com/ez-api/ez-api/internal/model"
+	"github.com/redis/go-redis/v9"
+)
+
+func TestLogWebhookServiceNotifyThreshold(t *testing.T) {
+	mr := miniredis.RunT(t)
+	rdb := redis.NewClient(&redis.Options{Addr: mr.Addr()})
+	svc := NewLogWebhookService(rdb)
+
+	var hits int64
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		atomic.AddInt64(&hits, 1)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	cfg := LogWebhookConfig{
+		Enabled:             true,
+		URL:                 srv.URL,
+		Threshold:           2,
+		WindowSeconds:       60,
+		CooldownSeconds:     300,
+		StatusCodeThreshold: 500,
+	}
+	if _, err := svc.SetConfig(context.Background(), cfg); err != nil {
+		t.Fatalf("set config: %v", err)
+	}
+
+	rec := model.LogRecord{StatusCode: 500, ErrorMessage: "upstream error"}
+	svc.NotifyIfNeeded(context.Background(), rec)
+	svc.NotifyIfNeeded(context.Background(), rec)
+
+	if atomic.LoadInt64(&hits) != 1 {
+		t.Fatalf("expected 1 webhook hit, got %d", hits)
+	}
+}
+
+func TestLogWebhookServiceDefaults(t *testing.T) {
+	mr := miniredis.RunT(t)
+	rdb := redis.NewClient(&redis.Options{Addr: mr.Addr()})
+	svc := NewLogWebhookService(rdb)
+
+	cfg, err := svc.GetConfig(context.Background())
+	if err != nil {
+		t.Fatalf("get config: %v", err)
+	}
+	if cfg.Threshold != defaultWebhookThreshold || cfg.WindowSeconds != defaultWebhookWindow {
+		t.Fatalf("unexpected defaults: %+v", cfg)
+	}
+}