feat(payment): 虎皮椒聚合支付 - 官方插件与跨平台可执行文件

新增 xunhupay 官方包，支付 RPC 与宿主只保留订单和验签边界；官方支付包同时带上各系统 provider，避免把 Linux ELF 当成本机入口。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/app/protocol_plugins.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"sort"
@@ -91,6 +92,15 @@ type pluginRegistryRecord struct {
 }
 
 func newPluginRuntime(dataDir string) (*pluginRuntime, error) {
+	dataDir = strings.TrimSpace(dataDir)
+	if dataDir == "" {
+		return nil, errors.New("plugin data directory is empty")
+	}
+	var err error
+	dataDir, err = filepath.Abs(dataDir)
+	if err != nil {
+		return nil, fmt.Errorf("plugin data directory is invalid: %w", err)
+	}
 	if err := os.MkdirAll(dataDir, 0o755); err != nil {
 		return nil, fmt.Errorf("create plugin registry directory: %w", err)
 	}
@@ -519,8 +529,24 @@ func paymentRuntimeReady(root, digest, backendEntry string) bool {
 	if err != nil || strings.TrimSpace(string(ready)) != digest {
 		return false
 	}
-	entry, err := os.Stat(filepath.Join(root, filepath.FromSlash(backendEntry)))
-	return err == nil && !entry.IsDir()
+	return protocol.HasAnyPaymentRPCBackend(backendEntry, paymentRuntimeBackendFiles(root))
+}
+
+func paymentRuntimeBackendFiles(root string) map[string][]byte {
+	files := map[string][]byte{}
+	backendRoot := filepath.Join(root, "backend")
+	_ = filepath.WalkDir(backendRoot, func(path string, entry fs.DirEntry, err error) error {
+		if err != nil || entry.IsDir() {
+			return err
+		}
+		rel, relErr := filepath.Rel(root, path)
+		if relErr != nil {
+			return nil
+		}
+		files[filepath.ToSlash(rel)] = []byte{1}
+		return nil
+	})
+	return files
 }
 
 func (c *pluginRuntime) list() []PluginView {