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>

test/field_help_test.dart

@@ -0,0 +1,89 @@
+// In-place help widgets + the satellite dialog that consumes them.
+// The pattern (usertest): explain a surface where it happens —
+// an intro strip saying what this is and what will happen, plus a
+// per-field "?" for the details.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_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 'package:chain_studio/widgets/chain_field_help.dart';
+
+import 'support/fake_hub.dart';
+
+Widget _host(Widget child) => MaterialApp(
+  localizationsDelegates: AppLocalizations.localizationsDelegates,
+  supportedLocales: AppLocalizations.supportedLocales,
+  locale: const Locale('de'),
+  home: Scaffold(body: child),
+);
+
+void main() {
+  testWidgets('ChainInlineHelp shows the text and fires Learn more', (
+    tester,
+  ) async {
+    var learned = false;
+    await tester.pumpWidget(
+      _host(
+        ChainInlineHelp(
+          text: 'Ein Satellit ist ein weiterer Hub.',
+          onLearnMore: () => learned = true,
+          learnMoreLabel: 'Mehr erfahren',
+        ),
+      ),
+    );
+    expect(find.text('Ein Satellit ist ein weiterer Hub.'), findsOneWidget);
+    await tester.tap(find.text('Mehr erfahren'));
+    expect(learned, isTrue);
+  });
+
+  testWidgets('ChainInlineHelp hides Learn more when no callback', (
+    tester,
+  ) async {
+    await tester.pumpWidget(
+      _host(const ChainInlineHelp(text: 'Nur Text, kein Link.')),
+    );
+    expect(find.text('Nur Text, kein Link.'), findsOneWidget);
+    expect(find.byIcon(Icons.arrow_forward), findsNothing);
+  });
+
+  testWidgets('ChainFieldHelp tap reveals the tooltip message', (tester) async {
+    await tester.pumpWidget(
+      _host(
+        const ChainFieldLabel(
+          label: 'Satelliten-Name',
+          help: 'Frei wählbarer Anzeigename.',
+        ),
+      ),
+    );
+    // The help text is not shown until the affordance is used.
+    expect(find.text('Frei wählbarer Anzeigename.'), findsNothing);
+    await tester.tap(find.byIcon(Icons.help_outline));
+    await tester.pump(const Duration(milliseconds: 400));
+    expect(find.text('Frei wählbarer Anzeigename.'), findsOneWidget);
+  });
+
+  testWidgets('Add-satellite dialog explains what a satellite is', (
+    tester,
+  ) async {
+    SharedPreferences.setMockInitialValues({});
+    installFakeHub();
+    await tester.pumpWidget(_host(const FederationPage()));
+    await tester.pump(const Duration(milliseconds: 200));
+
+    // Open the add flow via the AppBar action (the label also
+    // appears in the empty-state CTA; either opens the dialog).
+    await tester.tap(find.text('Satellit hinzufügen').first);
+    await tester.pumpAndSettle();
+
+    // The intro strip + its Learn-more link are present BEFORE any
+    // input is asked for — no more bare "name" field.
+    expect(find.textContaining('Ein Satellit ist ein weiterer Hub'),
+        findsOneWidget);
+    expect(find.text('Mehr erfahren'), findsOneWidget);
+    // Field-level "?" is wired too.
+    expect(find.byType(ChainFieldHelp), findsWidgets);
+  });
+}