feat(钉钉通道): 支持仅使用 access_token 配置钉钉机器人

Motivation:
钉钉机器人的 webhook 前缀固定不变，要求用户填写完整 URL 冗余且容易出错。简化通道配置项，降低接入配置成本，同时保证存量配置不受影响。

Changes:

* 钉钉通道配置改用 access_token，webhook 前缀由内部固定拼接
* 保留对旧 webhook_url 配置的兼容，access_token 存在时优先生效
* 新增 webhook 地址解析逻辑的单元测试，覆盖优先级与回退场景
* 同步更新 README、HTTP 请求示例及设计文档中的配置示例
* E2E 测试改用 E2E_DINGTALK_ACCESS_TOKEN 环境变量并按新格式创建通道

internal/adapter/dingtalk.go

@@ -13,9 +13,21 @@ import (
 	"time"
 )
 
+// 钉钉自定义机器人 webhook 前缀固定，配置时只需提供 access_token
+const dingtalkWebhookPrefix = "https://oapi.dingtalk.com/robot/send?access_token="
+
 type dingtalkConfig struct {
-	WebhookURL string `json:"webhook_url"`
-	Secret     string `json:"secret,omitempty"`
+	AccessToken string `json:"access_token"`
+	Secret      string `json:"secret,omitempty"`
+	// WebhookURL 兼容旧配置；新配置优先使用 AccessToken
+	WebhookURL string `json:"webhook_url,omitempty"`
+}
+
+func (c *dingtalkConfig) webhookURL() string {
+	if c.AccessToken != "" {
+		return dingtalkWebhookPrefix + c.AccessToken
+	}
+	return c.WebhookURL
 }
 
 type dingtalkMessage struct {
@@ -41,16 +53,16 @@ func (s *DingTalkSender) Send(title, content string, config json.RawMessage) err
 	}
 
 	if s.limiter != nil {
-		if err := s.limiter.Acquire(context.Background(), DingTalkLimitKey(cfg.WebhookURL)); err != nil {
+		if err := s.limiter.Acquire(context.Background(), DingTalkLimitKey(cfg.webhookURL())); err != nil {
 			return fmt.Errorf("dingtalk rate limit: %w", err)
 		}
 	}
 
-	reqURL := cfg.WebhookURL
+	reqURL := cfg.webhookURL()
 	if cfg.Secret != "" {
 		timestamp := time.Now().UnixMilli()
 		sign := dingtalkSign(timestamp, cfg.Secret)
-		reqURL = fmt.Sprintf("%s&timestamp=%d&sign=%s", cfg.WebhookURL, timestamp, sign)
+		reqURL = fmt.Sprintf("%s&timestamp=%d&sign=%s", reqURL, timestamp, sign)
 	}
 
 	msg := dingtalkMessage{

internal/adapter/dingtalk_test.go

@@ -0,0 +1,34 @@
+package adapter
+
+import "testing"
+
+func TestDingtalkConfigWebhookURL(t *testing.T) {
+	tests := []struct {
+		name    string
+		cfg     dingtalkConfig
+		wantURL string
+	}{
+		{
+			name:    "access token only",
+			cfg:     dingtalkConfig{AccessToken: "tok-abc"},
+			wantURL: "https://oapi.dingtalk.com/robot/send?access_token=tok-abc",
+		},
+		{
+			name:    "access token takes precedence over legacy url",
+			cfg:     dingtalkConfig{AccessToken: "tok-abc", WebhookURL: "https://legacy.example/webhook"},
+			wantURL: "https://oapi.dingtalk.com/robot/send?access_token=tok-abc",
+		},
+		{
+			name:    "fallback to legacy url",
+			cfg:     dingtalkConfig{WebhookURL: "https://legacy.example/webhook"},
+			wantURL: "https://legacy.example/webhook",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.cfg.webhookURL(); got != tt.wantURL {
+				t.Fatalf("webhookURL() = %q, want %q", got, tt.wantURL)
+			}
+		})
+	}
+}