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/base/contexts/AppContext.tsx

@@ -19,6 +19,7 @@ import { AppPageHistoryContextProvider } from '@/base/contexts/AppPageHistoryCon
 import { AppThemeContextProvider } from '@/features/theme/AppThemeContext.tsx';
 import { NavBarContextProvider } from '@/features/navigation-bar/NavbarContext.tsx';
 import { SessionContextProvider } from '@/features/authentication/SessionContext.tsx';
+import { SubpathConfig } from '@/lib/utils/SubpathConfig.ts';
 
 interface Props {
     children: React.ReactNode;
@@ -26,7 +27,7 @@ interface Props {
 
 export const AppContext: React.FC<Props> = ({ children }) => (
     <SessionContextProvider>
-        <Router>
+        <Router basename={SubpathConfig.getRouterBasename()}>
             <StyledEngineProvider injectFirst>
                 <AppThemeContextProvider>
                     <QueryParamProvider adapter={ReactRouter6Adapter}>