Add dynamic subpath support (#1011)

* Add dynamic subpath support for WebUI

- Add SubpathConfig utility for server-side subpath detection
- Configure React Router basename from server config
- Update API base URL handling for subpath compatibility
- Fix asset loading with relative paths
- Add VITE_SUBPATH environment variable for development
- Update locales and manifest paths for subpath support

Closes #174

* Move VITE_SUBPATH interface to vite-env.d.ts

* Ensure production bundle always uses relative base

src/lib/requests/client/BaseClient.ts

@@ -10,6 +10,7 @@ import { AppStorage } from '@/lib/storage/AppStorage.ts';
 import { UserRefreshMutation } from '@/lib/graphql/generated/graphql.ts';
 import { AuthManager } from '@/features/authentication/AuthManager.ts';
 import { AbortableApolloMutationResponse } from '@/lib/requests/RequestManager.ts';
+import { SubpathConfig } from '@/lib/utils/SubpathConfig.ts';
 
 export abstract class BaseClient<Client, ClientConfig, Fetcher> {
     protected abstract client: Client;
@@ -68,7 +69,10 @@ export abstract class BaseClient<Client, ClientConfig, Fetcher> {
             ? import.meta.env.VITE_SERVER_URL_DEFAULT
             : `${protocol}//${hostname}:${port}`;
 
-        return AppStorage.local.getItemParsed('serverBaseURL', defaultUrl);
+        const serverBaseURL = AppStorage.local.getItemParsed('serverBaseURL', defaultUrl);
+
+        // Apply subpath configuration to the base URL
+        return SubpathConfig.getApiBaseUrl(serverBaseURL);
     }
 
     public abstract updateConfig(config: Partial<ClientConfig>): void;