feat: implement role-based entry and navigation enhancements

- Replace credential login with Admin/Practitioner role selection
- Add role-switcher toggle in header with automatic reversion for Admin mode
- Implement immediate return to role selection via system logo click
- Integrate role state management into global app state

src/core/state.ts

@@ -38,6 +38,7 @@ export interface AppState {
   activeSubTab: string;
   masterData: MasterAssetData;
   activeCharts: any[];
+  currentUserRole: 'admin' | 'user';
 }
 
 // 초기 상태
@@ -45,6 +46,7 @@ export const state: AppState = {
   activeCategory: 'hw',
   activeSubTab: '서버', // 대시보드 제거됨에 따라 기본값 변경
   activeCharts: [],
+  currentUserRole: 'user',
   masterData: {
     users: [],
     pc: [], server: [], storage: [], network: [],