diff --git a/adminfront/src/components/layout/RoleSwitcher.tsx b/adminfront/src/components/layout/RoleSwitcher.tsx
index a173b7d5..68e299c4 100644
--- a/adminfront/src/components/layout/RoleSwitcher.tsx
+++ b/adminfront/src/components/layout/RoleSwitcher.tsx
@@ -63,7 +63,8 @@ const RoleSwitcher: FC = () => {
         border: "1px solid #333",
       }}
     >
-      <div
+      <button
+        type="button"
         style={{
           display: "flex",
           alignItems: "center",
@@ -73,6 +74,11 @@ const RoleSwitcher: FC = () => {
           fontWeight: "bold",
           paddingBottom: isCollapsed ? "0" : "4px",
           borderBottom: isCollapsed ? "none" : "1px solid #444",
+          background: "transparent",
+          border: "none",
+          width: "100%",
+          color: "inherit",
+          textAlign: "inherit",
         }}
         onClick={toggleCollapse}
       >
@@ -88,7 +94,7 @@ const RoleSwitcher: FC = () => {
           )}
         </div>
         {isCollapsed ? <ChevronUp size={14} /> : <ChevronDown size={14} />}
-      </div>
+      </button>
 
       {!isCollapsed && (
         <div
diff --git a/adminfront/src/features/tenants/routes/TenantGroupsPage.tsx b/adminfront/src/features/tenants/routes/TenantGroupsPage.tsx
index 6e62d938..74be752b 100644
--- a/adminfront/src/features/tenants/routes/TenantGroupsPage.tsx
+++ b/adminfront/src/features/tenants/routes/TenantGroupsPage.tsx
@@ -1,4 +1,8 @@
-import { useMutation, useQuery } from "@tanstack/react-query";
+import {
+  type UseMutationResult,
+  useMutation,
+  useQuery,
+} from "@tanstack/react-query";
 import type { AxiosError } from "axios";
 import {
   ChevronDown,
@@ -57,15 +61,15 @@ function buildGroupTree(
   const childrenOf = new Map<string, UserGroupNode[]>();
 
   // First pass: Initialize all groups as nodes and populate childrenOf map
-  groups.forEach((group) => {
+  for (const group of groups) {
     childrenOf.set(group.id, []);
-  });
+  }
 
   // Second pass: Populate children
-  groups.forEach((group) => {
+  for (const group of groups) {
     const node: UserGroupNode = {
       ...group,
-      children: childrenOf.get(group.id)!,
+      children: childrenOf.get(group.id) ?? [],
     };
     if (group.parentId === parentId) {
       nodes.push(node);
@@ -79,13 +83,13 @@ function buildGroupTree(
         nodes.push(node);
       }
     }
-  });
+  }
 
   // Sort children for consistent rendering (optional, but good for UI)
   nodes.sort((a, b) => a.name.localeCompare(b.name));
-  nodes.forEach((node) => {
+  for (const node of nodes) {
     node.children.sort((a, b) => a.name.localeCompare(b.name));
-  });
+  }
 
   return nodes;
 }
@@ -97,8 +101,16 @@ interface UserGroupTreeNodeProps {
   selectedGroupId: string | null;
   onDelete: (groupId: string) => void;
   onAddSubGroup: (parentId: string) => void;
-  addMemberMutation: any; // Simplified type for now
-  removeMemberMutation: any; // Simplified type for now
+  addMemberMutation: UseMutationResult<
+    void,
+    AxiosError<{ error?: string }>,
+    { groupId: string; userId: string }
+  >;
+  removeMemberMutation: UseMutationResult<
+    void,
+    AxiosError<{ error?: string }>,
+    { groupId: string; userId: string }
+  >;
 }
 
 const UserGroupTreeNode: React.FC<UserGroupTreeNodeProps> = ({
diff --git a/adminfront/src/features/tenants/routes/TenantListPage.tsx b/adminfront/src/features/tenants/routes/TenantListPage.tsx
index db652d75..78b850a2 100644
--- a/adminfront/src/features/tenants/routes/TenantListPage.tsx
+++ b/adminfront/src/features/tenants/routes/TenantListPage.tsx
@@ -38,7 +38,9 @@ function buildTenantTree(tenants: TenantSummary[]): TenantNode[] {
   }
 
   for (const tenant of tenants) {
-    const node = tenantMap.get(tenant.id)!;
+    const node = tenantMap.get(tenant.id);
+    if (!node) continue;
+
     if (tenant.parentId) {
       const parent = tenantMap.get(tenant.parentId);
       if (parent) {
diff --git a/adminfront/src/features/user-groups/routes/TenantUserGroupsTab.tsx b/adminfront/src/features/user-groups/routes/TenantUserGroupsTab.tsx
index 77a68415..942e0e00 100644
--- a/adminfront/src/features/user-groups/routes/TenantUserGroupsTab.tsx
+++ b/adminfront/src/features/user-groups/routes/TenantUserGroupsTab.tsx
@@ -50,23 +50,29 @@ function buildGroupTree(groups: GroupSummary[]): UserGroupNode[] {
   const nodeMap = new Map<string, UserGroupNode>();
   const rootNodes: UserGroupNode[] = [];
 
-  groups.forEach((group) => {
+  for (const group of groups) {
     nodeMap.set(group.id, { ...group, children: [] });
-  });
+  }
+
+  for (const group of groups) {
+    const node = nodeMap.get(group.id);
+    if (!node) continue;
 
-  groups.forEach((group) => {
-    const node = nodeMap.get(group.id)!;
     if (group.parentId && nodeMap.has(group.parentId)) {
-      const parent = nodeMap.get(group.parentId)!;
-      parent.children.push(node);
+      const parent = nodeMap.get(group.parentId);
+      if (parent) {
+        parent.children.push(node);
+      }
     } else {
       rootNodes.push(node);
     }
-  });
+  }
 
   const sortNodes = (nodes: UserGroupNode[]) => {
     nodes.sort((a, b) => a.name.localeCompare(b.name));
-    nodes.forEach((node) => sortNodes(node.children));
+    for (const node of nodes) {
+      sortNodes(node.children);
+    }
   };
   sortNodes(rootNodes);
 
@@ -227,7 +233,7 @@ export function TenantUserGroupsTab() {
       groupsQuery.refetch();
       if (
         selectedGroupId &&
-        selectedGroupId === (deleteMutation.variables as any)
+        selectedGroupId === deleteMutation.variables
       ) {
         setSelectedGroupId(null);
       }
diff --git a/adminfront/src/features/user-groups/routes/UserGroupDetailPage.tsx b/adminfront/src/features/user-groups/routes/UserGroupDetailPage.tsx
index 89270480..59091292 100644
--- a/adminfront/src/features/user-groups/routes/UserGroupDetailPage.tsx
+++ b/adminfront/src/features/user-groups/routes/UserGroupDetailPage.tsx
@@ -1,4 +1,5 @@
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import type { AxiosError } from "axios";
 import { ArrowLeft, Shield, Trash2, UserPlus, Users } from "lucide-react";
 import { useState } from "react";
 import { Link, useParams } from "react-router-dom";
@@ -62,14 +63,13 @@ export function UserGroupDetailPage() {
   const [selectedTargetTenantId, setSelectedTargetTenantId] = useState("");
   const [selectedRelation, setSelectedRelation] = useState("view");
 
-  // Fetch specific group details
   const {
     data: currentGroup,
     isLoading: isGroupLoading,
     error,
   } = useQuery({
     queryKey: ["user-group-detail", id],
-    queryFn: () => fetchGroup(tenantId!, id!),
+    queryFn: () => fetchGroup(tenantId ?? "", id ?? ""),
     enabled: !!id && !!tenantId,
     retry: false,
   });
@@ -77,7 +77,7 @@ export function UserGroupDetailPage() {
   // Fetch assigned roles
   const { data: groupRoles, isLoading: isRolesLoading } = useQuery({
     queryKey: ["user-group-roles", id],
-    queryFn: () => fetchGroupRoles(tenantId!, id!),
+    queryFn: () => fetchGroupRoles(tenantId ?? "", id ?? ""),
     enabled: !!id && !!tenantId,
   });
 
@@ -96,7 +96,7 @@ export function UserGroupDetailPage() {
   });
 
   const addMemberMutation = useMutation({
-    mutationFn: (userId: string) => addGroupMember(tenantId!, id!, userId),
+    mutationFn: (userId: string) => addGroupMember(tenantId ?? "", id ?? "", userId),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["user-group-detail", id] });
       setIsAddMemberOpen(false);
@@ -105,15 +105,17 @@ export function UserGroupDetailPage() {
         t("msg.admin.groups.members.add_success", "구성원이 추가되었습니다."),
       );
     },
-    onError: (error: any) => {
+    onError: (error: AxiosError<{ error?: string }>) => {
       toast.error(
-        error.message || t("err.common.unknown", "오류가 발생했습니다."),
+        error.response?.data?.error ||
+          error.message ||
+          t("err.common.unknown", "오류가 발생했습니다."),
       );
     },
   });
 
   const removeMemberMutation = useMutation({
-    mutationFn: (userId: string) => removeGroupMember(tenantId!, id!, userId),
+    mutationFn: (userId: string) => removeGroupMember(tenantId ?? "", id ?? "", userId),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["user-group-detail", id] });
       toast.success(
@@ -127,7 +129,7 @@ export function UserGroupDetailPage() {
 
   const assignRoleMutation = useMutation({
     mutationFn: () =>
-      assignGroupRole(tenantId!, id!, selectedTargetTenantId, selectedRelation),
+      assignGroupRole(tenantId ?? "", id ?? "", selectedTargetTenantId, selectedRelation),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["user-group-roles", id] });
       setIsAddRoleOpen(false);
@@ -135,16 +137,18 @@ export function UserGroupDetailPage() {
         t("msg.admin.groups.roles.assign_success", "역할이 할당되었습니다."),
       );
     },
-    onError: (error: any) => {
+    onError: (error: AxiosError<{ error?: string }>) => {
       toast.error(
-        error.message || t("err.common.unknown", "오류가 발생했습니다."),
+        error.response?.data?.error ||
+          error.message ||
+          t("err.common.unknown", "오류가 발생했습니다."),
       );
     },
   });
 
   const removeRoleMutation = useMutation({
     mutationFn: (role: { targetTenantId: string; relation: string }) =>
-      removeGroupRole(tenantId!, id!, role.targetTenantId, role.relation),
+      removeGroupRole(tenantId ?? "", id ?? "", role.targetTenantId, role.relation),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["user-group-roles", id] });
       toast.success(
@@ -172,8 +176,8 @@ export function UserGroupDetailPage() {
         <div className="p-4 bg-destructive/10 text-destructive rounded-md text-left text-sm font-mono overflow-auto max-w-xl mx-auto border border-destructive/20">
           <p>
             Error:{" "}
-            {(error as any)?.response?.data?.error ||
-              (error as any)?.message ||
+            {(error as AxiosError<{ error?: string }>)?.response?.data?.error ||
+              error.message ||
               "Not found"}
           </p>
         </div>