feat(ui): remove in-app entity switcher, entity fixed at login

- MainLayout/ReportCenter: drop switch-entity switcher, keep read-only entity tag
- KPIList/PredictDashboard/GrowthQuality: entity selectors locked to session entity
- api/index.ts: drop switchEntity/myEntities wrappers (endpoint kept for compat)
- sidebar brand now shows logged-in entity name

(cma-remove-inapp-entity-switcher-20260914)

frontend/src/api/index.ts

@@ -38,8 +38,6 @@ api.interceptors.response.use(
 export const authApi = {
   login: (data: any) => api.post('/auth/login', data),
   register: (data: any) => api.post('/auth/register', data),
-  switchEntity: (data: any) => api.post('/auth/switch-entity', data),
-  myEntities: () => api.get('/auth/my-entities'),
   loginEntities: (username: string) => api.get('/auth/login-entities', { params: { username } }),
 }