feat(docs): in-place help pattern — explain a surface where it happens

New ChainInlineHelp (intro strip: what this is + what will happen, with
an optional 'Learn more' into the doc sheet) and ChainFieldHelp /
ChainFieldLabel (a '?' affordance per field). First applied to the
add-satellite dialog, which asked for a bare 'name' with no hint of
what a satellite is or does (usertest): it now leads with a plain
explanation + a federation 'Learn more', and the name field carries a
'?'. Both widgets are quiet by design.

Verified: field_help_test covers the widgets + that the dialog explains
itself; dialog_shots_test.dart (a reusable headed dialog-capture
harness) proved the layout in light + dark. Studio 0.76.0.

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

integration_test/dialog_shots_test.dart

@@ -0,0 +1,79 @@
+// Dialog capture harness — visual proof for dialogs the page-level
+// guide harness doesn't reach. Renders the target dialog against
+// the scriptable fake hub and writes a PNG per theme via a
+// RepaintBoundary (driverless, headed macOS `flutter test`).
+//
+//   flutter test integration_test/dialog_shots_test.dart -d macos
+//
+// Output: build/dialog-shots/<name>-<theme>.png (or $DIALOG_SHOTS_OUT).
+
+import 'dart:io';
+import 'dart:ui' as ui;
+
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:chain_studio/l10n/app_localizations.dart';
+import 'package:chain_studio/pages/federation.dart';
+
+import '../test/support/fake_hub.dart';
+
+final GlobalKey _shotKey = GlobalKey();
+
+String get _outDir =>
+    Platform.environment['DIALOG_SHOTS_OUT'] ?? 'build/dialog-shots';
+
+Future<void> _shot(WidgetTester tester, String name) async {
+  await tester.pump(const Duration(milliseconds: 150));
+  await tester.pump(const Duration(milliseconds: 150));
+  final boundary =
+      _shotKey.currentContext!.findRenderObject() as RenderRepaintBoundary;
+  final image = await boundary.toImage(pixelRatio: 2.0);
+  final bytes = await image.toByteData(format: ui.ImageByteFormat.png);
+  image.dispose();
+  final file = File('$_outDir/$name.png');
+  file.parent.createSync(recursive: true);
+  file.writeAsBytesSync(bytes!.buffer.asUint8List());
+  // ignore: avoid_print
+  print('dialog-shot: ${file.path}');
+}
+
+void main() {
+  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
+
+  for (final (themeName, mode) in [
+    ('light', ThemeMode.light),
+    ('dark', ThemeMode.dark),
+  ]) {
+    testWidgets('add-satellite dialog — $themeName', (tester) async {
+      SharedPreferences.setMockInitialValues({});
+      installFakeHub();
+      await tester.pumpWidget(
+        MaterialApp(
+          debugShowCheckedModeBanner: false,
+          themeMode: mode,
+          theme: ThemeData.light(useMaterial3: true),
+          darkTheme: ThemeData.dark(useMaterial3: true),
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          locale: const Locale('de'),
+          // Wrap the whole navigator (incl. the overlay dialogs
+          // render into) so the capture catches the dialog, not
+          // just the page beneath it.
+          builder: (context, child) =>
+              RepaintBoundary(key: _shotKey, child: child),
+          home: const FederationPage(),
+        ),
+      );
+      await tester.pump(const Duration(milliseconds: 200));
+      await tester.tap(find.text('Satellit hinzufügen').first);
+      await tester.pumpAndSettle();
+      await _shot(tester, 'add-satellite-$themeName');
+      expect(find.textContaining('Ein Satellit ist ein weiterer Hub'),
+          findsOneWidget);
+    });
+  }
+}