refactor: config + lldaplib 收敛到 LLDAP 形态（读只读、删 OpenLDAP 写路径与密码包）

- config 重写：删 user-ou/inactive-ou/group-root-* / group-object-class /
  group-member-attr / initial-password；新增 lldap 写通道 + webhook + confirm-base-url
  + 两套 schedule + guard
- ldaplib 收拢为只读：属性常量/DN 归入 attrs.go；删 ops.go 写路径与 internal/password
- config.example.yml 重写成 LLDAP 形态
- 组命名修订（呼应 AGENTS.md 约束12）：用部门稳定索引 cn=<dept_id> 做组身份，
  mirror_departments 增 group_id 列并跨快照保留，可读中文名只走 DB 展示

internal/syncer/snapshot.go

@@ -101,10 +101,8 @@ func (r *SnapshotRunner) RunSnapshot(ctx context.Context) (*SnapshotRunResult, e
 
 // buildMirror 把飞书快照转成镜像存储层需要的输入。
 //
-// 部门拍平命名与 DN 由 mapping.FlatDeptInfo 一次性算好并持久化到
-// mirror_departments，物化阶段直接复用、WebUI 亦可展示。
+// 部门组 DN 用稳定索引派生（mapping.DeptGroupDN），可读中文名只落 name 列供展示。
 func (r *SnapshotRunner) buildMirror(snap *feishu.Snapshot) *store.MirrorSnapshot {
-	flat := mapping.FlatDeptInfo(snap.Departments, r.cfg.Ldap.BaseDN)
 	deptName := make(map[string]string, len(snap.Departments))
 	for _, d := range snap.Departments {
 		deptName[d.ID] = d.Name
@@ -112,10 +110,9 @@ func (r *SnapshotRunner) buildMirror(snap *feishu.Snapshot) *store.MirrorSnapsho
 
 	depts := make([]*store.MirrorDepartment, 0, len(snap.Departments))
 	for _, d := range snap.Departments {
-		f := flat[d.ID]
 		depts = append(depts, &store.MirrorDepartment{
-			DeptID: d.ID, Name: d.Name, PinyinName: f.Chain, DN: f.DN,
-			ParentID: d.ParentID, Level: f.Level, State: store.StateActive,
+			DeptID: d.ID, Name: d.Name, DN: mapping.DeptGroupDN(d.ID, r.cfg.Ldap.BaseDN),
+			ParentID: d.ParentID, Level: deptLevel(d.ID, snap.Departments), State: store.StateActive,
 		})
 	}
 
@@ -144,6 +141,28 @@ func (r *SnapshotRunner) buildMirror(snap *feishu.Snapshot) *store.MirrorSnapsho
 	return &store.MirrorSnapshot{Users: users, Departments: depts, Skipped: skipped}
 }
 
+// deptLevel 计算部门在树中的层级，根为 0。带步数上限防环。
+func deptLevel(id string, depts []*feishu.Department) int {
+	byID := make(map[string]*feishu.Department, len(depts))
+	for _, d := range depts {
+		byID[d.ID] = d
+	}
+	depth := 0
+	cur := id
+	for i := 0; i < 64; i++ {
+		d, ok := byID[cur]
+		if !ok || d.ParentID == "" || d.ParentID == "0" {
+			return depth
+		}
+		if _, ok := byID[d.ParentID]; !ok {
+			return depth // 父不在同步范围内，视为根
+		}
+		depth++
+		cur = d.ParentID
+	}
+	return depth
+}
+
 // toMirrorUser 把飞书用户域模型转成镜像用户。字段语义与 mapping 一致，
 // business_category 展开为部门中文名便于人工阅读。
 func toMirrorUser(u *feishu.User, uid string, deptName map[string]string) *store.MirrorUser {