feat(settings): migrate Export All Keys modal to the reference design

Phase 1. DialogWarningHeader care header (was a hand-rolled red icon+text);
centered DialogActionFooter (Export + Close) replacing the StyledButtons + two
separators; on full success the saved path shows in a copy field with a green
check, partial/error render inline; export progress uses LoadingDots. Full i18n:
the previously-hardcoded notification + status strings now use TR (8 new
export_keys_* keys in en + 8 langs). Added hide() + a modal-export-all-keys sweep
surface. Also fixes a latent Begin/EndOverlayDialog imbalance on the 0-address
early return. No change to the export RPC logic.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/export_all_keys_dialog.h

@@ -27,6 +27,9 @@ public:
     
     // Check if dialog is open
     static bool isOpen();
+
+    // Close the dialog (used by the UI sweep teardown)
+    static void hide();
 };
 
 } // namespace ui