feat(qbz-ui): settings export modal + Developer row (04 §4.2)

Add the desktop "Export settings…" surface for the qbzd daemon epic (T18):
a Developer-settings row that opens a modal with the single default-off
"Include Qobuz login and integration tokens" gate, its warning line, and a
Cancel/Export footer. Confirm() is a Rust callback (wired next). New
SettingsExportState/SettingsExportActions globals, exported from app.slint
so the Rust layer binds them, and the modal mounted in AppShell. New strings
translated across all 8 locales (en es de fr pt ru ja nl).

cc

crates/qbz-ui/ui/settings/DeveloperSettings.slint

@@ -6,7 +6,7 @@
 import { Theme } from "../foundation/semantic-colors.slint";
 import { Typography } from "../foundation/typography.slint";
 import { Radius } from "../foundation/radius.slint";
-import { QconnectDevState, LogViewerState } from "../state.slint";
+import { QconnectDevState, LogViewerState, SettingsExportState } from "../state.slint";
 import { SettingRow } from "SettingRow.slint";
 import { DiagnosticsPanel } from "DiagnosticsPanel.slint";
 
@@ -74,5 +74,20 @@ export component DeveloperSettings inherits VerticalLayout {
         }
     }
 
+    GroupHeader { text: @tr("SETTINGS PORTABILITY"); }
+
+    SettingRow {
+        label: @tr("Export settings…");
+        description: @tr("Save a portable bundle of your settings to move to another machine or the qbzd daemon.");
+        SecondaryButton {
+            label: @tr("Export…");
+            clicked => {
+                // Always reset the auth gate so it opens default-OFF (04 §4.2).
+                SettingsExportState.include-auth = false;
+                SettingsExportState.open = true;
+            }
+        }
+    }
+
     DiagnosticsPanel { }
 }