fix: 审批流程编辑器按步骤类型过滤可选用户

- 审核阶段: 只显示 admin/superadmin/dba/auditor 角色用户
- 执行阶段: 只显示 admin/superadmin/dba 角色用户
- 全选按钮也基于过滤后的用户列表
- UserDropdown 改用 fixed 定位避免 overflow 裁剪

frontend/src/pages/WorkflowPage.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect, useCallback, useRef } from 'react';
 import {
   Plus, Edit2, Eye, ToggleLeft, ToggleRight, GitBranch, Users, CheckCircle,
   ArrowRight, Shield, Trash2, X, ChevronDown, ChevronUp,
@@ -99,15 +99,30 @@ interface UserDropdownProps {
 
 function UserDropdown({ users, selectedIds, label, onToggle, onToggleAll, onClear, getUserName }: UserDropdownProps) {
   const [open, setOpen] = useState(false);
+  const triggerRef = useRef<HTMLButtonElement>(null);
   const ids = Array.isArray(selectedIds) ? selectedIds : [];
   const allSelected = ids.length === users.length && users.length > 0;
+  const [dropdownPos, setDropdownPos] = useState({ top: 0, left: 0, width: 0 });
+
+  const updatePos = () => {
+    if (triggerRef.current) {
+      const rect = triggerRef.current.getBoundingClientRect();
+      setDropdownPos({ top: rect.bottom + 4, left: rect.left, width: rect.width });
+    }
+  };
+
+  const handleToggle = () => {
+    if (!open) updatePos();
+    setOpen(!open);
+  };
 
   return (
     <div className="relative">
       {/* Trigger */}
       <button
+        ref={triggerRef}
         type="button"
-        onClick={() => setOpen(!open)}
+        onClick={handleToggle}
         className={`w-full flex items-center justify-between px-3 py-2 rounded-lg text-sm transition-colors ${
           selectedIds.length === 0
             ? 'bg-[var(--dg-bg-tertiary)] border border-red-500/40 text-[var(--dg-text-muted)]'
@@ -142,11 +157,14 @@ function UserDropdown({ users, selectedIds, label, onToggle, onToggleAll, onClea
         </div>
       )}
 
-      {/* Dropdown */}
+      {/* Dropdown — fixed positioning to escape overflow clipping */}
       {open && (
         <>
           <div className="fixed inset-0 z-40" onClick={() => setOpen(false)} />
-          <div className="absolute left-0 right-0 top-full mt-1 z-50 bg-[var(--dg-bg-secondary)] border border-[var(--dg-border)] rounded-lg shadow-xl max-h-52 overflow-y-auto">
+          <div
+            className="fixed z-50 bg-[var(--dg-bg-secondary)] border border-[var(--dg-border)] rounded-lg shadow-xl max-h-52 overflow-y-auto"
+            style={{ top: dropdownPos.top, left: dropdownPos.left, width: dropdownPos.width }}
+          >
             {/* Select all / Clear */}
             <div className="flex items-center justify-between px-3 py-2 border-b border-[var(--dg-border)]">
               <button
@@ -262,12 +280,20 @@ function WorkflowEditorModal({ workflow, users, onClose, onSaved }: EditorProps)
     });
   };
 
+  const getEligibleUsers = (stepType: string) => {
+    if (stepType === 'audit') return users.filter(u => ['admin', 'superadmin', 'dba', 'auditor'].includes(u.role));
+    if (stepType === 'execute') return users.filter(u => ['admin', 'superadmin', 'dba'].includes(u.role));
+    return users;
+  };
+
   const toggleAllUsers = (idx: number) => {
     const step = steps[idx];
-    if (step.approver_ids.length === users.length) {
+    const eligible = getEligibleUsers(step.step_type);
+    const allSelected = step.approver_ids.length === eligible.length && eligible.length > 0;
+    if (allSelected) {
       updateStep(idx, { approver_ids: [] });
     } else {
-      updateStep(idx, { approver_ids: users.map((u) => u.id) });
+      updateStep(idx, { approver_ids: eligible.map((u) => u.id) });
     }
   };
 
@@ -417,7 +443,7 @@ function WorkflowEditorModal({ workflow, users, onClose, onSaved }: EditorProps)
                     {step.step_type !== 'submit' && (
                       <div className="pl-9 mt-2">
                         <UserDropdown
-                          users={users}
+                          users={getEligibleUsers(step.step_type)}
                           selectedIds={step.approver_ids}
                           label={step.step_type === 'audit' ? '审核人员' : '执行人员'}
                           onToggle={(uid) => toggleUser(idx, uid)}