feat: add new fullscreen dialog UI, dialog manager and system self-check functionality

- Implement FSDialog component for system-wide dialogs
- Add dialog manager utility for centralized dialog control
- Introduce system self-check API and handle results
- Show welcome dialog for new superusers
- Display self-check errors on home page
- Refactor proxy form handling in InstanceDetail

src/api/index.js

@@ -36,6 +36,7 @@ export const systemApi = {
     getStatus: () => api.get('/system/getStatus'),
     getSoftwareInfo: () => api.get('/system/getSoftwareInfo'),
     getSystemInfo: () => api.get('/system/info'),
+    selfCheck: () => api.get('/system/selfCheck'),
     getSettings: (key) => {
         const url = key ? `/system/settings/get?key=${key}` : '/system/settings/get';
         return api.get(url);