fix(ui): keep main window closable after a native dialog on Windows (#6319)

A native Windows MessageBox attached to a parent window disables that
window (WS_DISABLED) for its lifetime and re-enables it on dismissal.
When the parent is the main window — whose WindowClosing hook hides
instead of closes — the enable/hide sequence races and leaves the window
unable to process its close (X) button afterwards, so e.g. a rejected
login error dialog left the main window stuck open.

Route all native dialogs through src/lib/dialogs.ts, which forces
Detached: true on Windows (NULL owner, no window ever disabled) and is a
no-op on macOS/Linux (keeps the attached sheet-style presentation).

client/ui/frontend/src/components/LanguagePicker.tsx

@@ -3,7 +3,7 @@ import { useTranslation } from "react-i18next";
 import * as Popover from "@radix-ui/react-popover";
 import * as ScrollArea from "@radix-ui/react-scroll-area";
 import { Command } from "cmdk";
-import { Dialogs } from "@wailsio/runtime";
+import { errorDialog } from "@/lib/dialogs.ts";
 import { CheckIcon, ChevronDown, Search } from "lucide-react";
 import { Preferences } from "@bindings/services";
 import { LanguageCode, type Language } from "@bindings/i18n/models.js";
@@ -90,7 +90,7 @@ export function LanguagePicker() {
         try {
             await Preferences.SetLanguage(code as LanguageCode);
         } catch (e) {
-            await Dialogs.Error({
+            await errorDialog({
                 Title: t("settings.error.saveTitle"),
                 Message: formatErrorMessage(e),
             });