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。

web/api/result_test.go

@@ -0,0 +1,31 @@
+//go:build web
+
+package api
+
+import "testing"
+
+func TestExtractHostPortIPv6(t *testing.T) {
+	tests := []struct {
+		name     string
+		target   string
+		wantHost string
+		wantPort string
+	}{
+		{name: "ipv4", target: "192.168.1.1:80", wantHost: "192.168.1.1", wantPort: "80"},
+		{name: "hostname", target: "example.com:443", wantHost: "example.com", wantPort: "443"},
+		{name: "bracketed ipv6", target: "[2001:db8::1]:8443", wantHost: "2001:db8::1", wantPort: "8443"},
+		{name: "bare ipv6 without port", target: "2001:db8::1", wantHost: "2001:db8::1", wantPort: ""},
+		{name: "invalid port", target: "example.com:abc", wantHost: "example.com:abc", wantPort: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := extractHost(tt.target); got != tt.wantHost {
+				t.Fatalf("extractHost(%q) = %q, want %q", tt.target, got, tt.wantHost)
+			}
+			if got := extractPort(tt.target); got != tt.wantPort {
+				t.Fatalf("extractPort(%q) = %q, want %q", tt.target, got, tt.wantPort)
+			}
+		})
+	}
+}