feat: 统一服务缓存 + 指纹驱动插件匹配

将 webServiceCache 扩展为通用 serviceCache，所有指纹识别结果
统一缓存，插件匹配时端口不命中则回退到服务名称匹配。

删除多余的 service_cache.go，复用已有的 ServiceInfo 体系。
补充 nil 防御、Explicit 标记、大量单元/集成/回归测试。

webscan/web_scan_test.go

@@ -134,6 +134,26 @@ func TestBuildTargetURL(t *testing.T) {
 			expected:    "http://[2001:db8::1]:443",
 			expectError: false,
 		},
+		{
+			name: "bare ipv6 url without protocol gets brackets",
+			hostInfo: &common.HostInfo{
+				Host: "2001:db8::1",
+				Port: 80,
+				URL:  "2001:db8::1/admin",
+			},
+			expected:    "http://[2001:db8::1]",
+			expectError: false,
+		},
+		{
+			name: "bare ipv6 url with protocol gets brackets",
+			hostInfo: &common.HostInfo{
+				Host: "2001:db8::1",
+				Port: 80,
+				URL:  "http://2001:db8::1/admin",
+			},
+			expected:    "http://[2001:db8::1]",
+			expectError: false,
+		},
 	}
 
 	for _, tt := range tests {