fix: filter out nodes missing server/port before rendering

Nodes with port=0 or empty server cause client-side errors (e.g.
sing-box decode config failures). Filter them at the render dispatch
layer so all targets (sing-box, mihomo, surge, etc.) are protected.

internal/render/dispatch.go

@@ -9,9 +9,28 @@ import (
 	"github.com/peterqiu0516/sub-store/internal/util"
 )
 
+// filterInvalidProxies removes nodes missing required server/port fields.
+// These would cause client-side errors (e.g. sing-box "missing server_port").
+func filterInvalidProxies(proxies []model.ProxyNode) []model.ProxyNode {
+	result := make([]model.ProxyNode, 0, len(proxies))
+	for _, p := range proxies {
+		if p == nil {
+			continue
+		}
+		server := getString(p, "server")
+		port := getInt(p, "port")
+		if server == "" || port <= 0 {
+			continue
+		}
+		result = append(result, p)
+	}
+	return result
+}
+
 // RenderTarget dispatches to the appropriate renderer based on target.
 // This is the simplified entry point matching renderTarget() in the reference.
 func RenderTarget(proxies []model.ProxyNode, target string, template map[string]any) (string, error) {
+	proxies = filterInvalidProxies(proxies)
 	if len(proxies) == 0 {
 		return "", fmt.Errorf("No supported nodes for %s output", target)
 	}
@@ -45,6 +64,10 @@ func RenderTarget(proxies []model.ProxyNode, target string, template map[string]
 
 // RenderBuildTarget dispatches with a request URL for mihomo source comments.
 func RenderBuildTarget(proxies []model.ProxyNode, target string, requestUrl string, template map[string]any) (string, error) {
+	proxies = filterInvalidProxies(proxies)
+	if len(proxies) == 0 {
+		return "", fmt.Errorf("No supported nodes for %s output", target)
+	}
 	switch target {
 	case model.TargetMihomo, model.TargetStash:
 		return RenderMihomoYaml(proxies, requestUrl, template), nil