feat(studio): show a source module's data terms before the install button

The store detail sheet now carries a data-source block for source.*
modules: publisher, upstream url, the terms in plain words, and any
attribution the operator has to carry with the output. It sits above
maintainers and above the install button, because it is a decision
input rather than a footnote.

The values are selectable: compliance notes get written by copying,
not retyping. A note names whose terms these are, so nobody reads them
as the module's own licence. Four guards, including that an empty
attribution renders no empty row.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

test/store_data_source_test.dart

@@ -0,0 +1,85 @@
+// Guards for the data-provenance block in the store detail sheet.
+//
+// The rule it protects (docs/architecture/store-format.md): the terms
+// of the material a source module fetches are separate from the
+// module's own licence, and an operator must see them before the
+// install button, not in a README afterwards.
+
+import 'package:chain_studio/data/hub.dart';
+import 'package:chain_studio/l10n/app_localizations.dart';
+import 'package:chain_studio/pages/store.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Widget _host(Widget child) => MaterialApp(
+      localizationsDelegates: AppLocalizations.localizationsDelegates,
+      supportedLocales: AppLocalizations.supportedLocales,
+      locale: const Locale('de'),
+      home: Scaffold(body: SingleChildScrollView(child: child)),
+    );
+
+void main() {
+  const bund = DataProvenance(
+    name: 'gesetze-im-internet.de (BMJ / juris GmbH)',
+    url: 'https://www.gesetze-im-internet.de/',
+    license: 'Amtliches Werk (§ 5 UrhG), gemeinfrei',
+    attribution: 'Quelle: gesetze-im-internet.de (Bundesministerium der Justiz)',
+  );
+
+  testWidgets('publisher, terms and attribution are all shown',
+      (tester) async {
+    await tester.pumpWidget(_host(const StoreDataSourceSection(source: bund)));
+    await tester.pumpAndSettle();
+
+    expect(find.text(bund.name), findsOneWidget);
+    expect(find.text(bund.url), findsOneWidget);
+    expect(find.text(bund.license), findsOneWidget);
+    expect(find.text(bund.attribution), findsOneWidget,
+        reason: 'an attribution duty must be visible before installing');
+  });
+
+  testWidgets('the attribution row is omitted when none is required',
+      (tester) async {
+    const noAttribution = DataProvenance(
+      name: 'Vom Betreiber gepflegter Metadaten-Katalog',
+      url: '',
+      license: 'Katalog des Betreibers',
+      attribution: '',
+    );
+    await tester
+        .pumpWidget(_host(const StoreDataSourceSection(source: noAttribution)));
+    await tester.pumpAndSettle();
+
+    expect(find.text(noAttribution.name), findsOneWidget);
+    final l = AppLocalizations.of(
+      tester.element(find.byType(StoreDataSourceSection)),
+    )!;
+    expect(find.text(l.storeDataSourceAttribution), findsNothing,
+        reason: 'an empty attribution must not render an empty row');
+  });
+
+  testWidgets('the terms are selectable so they can be copied',
+      (tester) async {
+    await tester.pumpWidget(_host(const StoreDataSourceSection(source: bund)));
+    await tester.pumpAndSettle();
+
+    // Compliance notes get written by copying, not retyping.
+    expect(
+      find.byWidgetPredicate(
+        (w) => w is SelectableText && w.data == bund.attribution,
+      ),
+      findsOneWidget,
+    );
+  });
+
+  testWidgets('the note says whose terms these are', (tester) async {
+    await tester.pumpWidget(_host(const StoreDataSourceSection(source: bund)));
+    await tester.pumpAndSettle();
+
+    final l = AppLocalizations.of(
+      tester.element(find.byType(StoreDataSourceSection)),
+    )!;
+    // Without this line an operator reads the terms as the module's.
+    expect(find.text(l.storeDataSourceNote), findsOneWidget);
+  });
+}