fix(权限): 修复业务接入预览权限映射

业务接入预览属于只读预演，不应要求执行导入权限。\n将预览接口映射到 tplus:preview，并增加路由权限回归，避免只读角色被错误拒绝。\n\n影响范围：T+ 工作台业务接入预览接口与权限策略。\n\nCo-Authored-By: Claude Code <noreply@anthropic.com>

backend/app/services/authorization_policy.py

@@ -58,6 +58,8 @@ def permission_for(module, name, method, *, params=None, body=None):
     if module == "system.tplus":
         return "tplus:" + ("view" if method == "GET" else "retry" if name == "retry" else "collect")
     if module == "system.tplus_workbench":
+        if name == "business_sync_preview":
+            return "tplus:preview"
         if name.startswith("business_sync_"):
             return "tplus:view" if method == "GET" else "tplus:import"
         if name == "work_report":