feat: close modals with browser back button on mobile (#257)

* feat: close modals with browser back button on mobile

Create reusable useModalHistory hook that pushes history state when a
modal opens and listens for popstate to close it. Apply to ReportModal,
ClearMissedConfirm, ExportModal, ImportConfirm, and all modals using
ConfirmModal/ShareDialog/Auth/ExportModal base components. Escape key
handling was already in place for desktop.

Closes #253

* fix: update tests for renamed button labels and missing useModalHistory mock

frontend/src/test/components/ShareDialog.test.tsx

@@ -54,7 +54,8 @@ describe("ShareDialog", () => {
 
 	it("calls onClose when close button is clicked", () => {
 		render(<ShareDialog {...defaultProps} />);
-		fireEvent.click(screen.getByRole("button", { name: /common\.close/i }));
+		const closeButtons = screen.getAllByRole("button", { name: /common\.close/i });
+		fireEvent.click(closeButtons[closeButtons.length - 1]);
 		expect(defaultProps.onClose).toHaveBeenCalled();
 	});