Show action buttons in export previews

QLPreviewController only renders its share, print and open-in actions
when it is inside a navigation controller, so diagram and report
previews were dead ends. Wrap it in one, add an explicit Done button
and assert both in a UI test.

CableUITestsScreenshot/SystemExportButtonUITests.swift

@@ -40,6 +40,50 @@ final class SystemExportButtonUITests: XCTestCase {
         )
     }
 
+    @MainActor
+    func testReportPreviewOffersActionButtons() throws {
+        let app = launch(arguments: ["--uitest-reset-data", "--uitest-sample-data"])
+
+        openFirstSystem(in: app)
+
+        let shareButton = app.buttons["system-overview-share-button"]
+        XCTAssertTrue(shareButton.waitForExistence(timeout: 15))
+        shareButton.tap()
+
+        let reportItem = app.buttons.matching(
+            NSPredicate(format: "label CONTAINS[c] 'PDF'")
+        ).firstMatch
+        XCTAssertTrue(reportItem.waitForExistence(timeout: 10))
+        reportItem.tap()
+
+        // Quick Look lives in its own navigation stack; the Done button proves
+        // the navigation bar exists, the share item proves the file can leave
+        // the preview.
+        let doneButton = app.buttons["quick-look-done-button"]
+        XCTAssertTrue(
+            doneButton.waitForExistence(timeout: 60),
+            "Quick Look preview must be embedded in a navigation bar"
+        )
+
+        // Scope the action lookup to the preview's own navigation bar so the
+        // Overview share button underneath can never satisfy it.
+        let previewBar = app.navigationBars.containing(
+            .button,
+            identifier: "quick-look-done-button"
+        ).firstMatch
+        XCTAssertTrue(previewBar.waitForExistence(timeout: 10))
+
+        let actionButtons = previewBar.buttons.allElementsBoundByIndex
+            .filter { $0.identifier != "quick-look-done-button" }
+        XCTAssertFalse(
+            actionButtons.isEmpty,
+            "Quick Look preview must offer an action button to share or open the file"
+        )
+
+        doneButton.tap()
+        XCTAssertTrue(shareButton.waitForExistence(timeout: 10))
+    }
+
     // MARK: - Helpers
 
     private func launch(arguments: [String]) -> XCUIApplication {