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>

lib/pages/federation.dart

@@ -61,13 +61,38 @@ class _FederationPageState extends State<FederationPage> {
       context: context,
       builder: (ctx) => AlertDialog(
         title: Text(l.federationAddDialogTitle),
-        content: TextField(
-          controller: controller,
-          autofocus: true,
-          decoration: InputDecoration(
-            labelText: l.federationNameLabel,
-            hintText: 'satellite-a',
-            border: const OutlineInputBorder(),
+        content: ConstrainedBox(
+          constraints: const BoxConstraints(maxWidth: 420),
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              // Say what this is and what will happen before asking
+              // for input — a bare "name" field left the operator
+              // guessing what a satellite even is (usertest).
+              ChainInlineHelp(
+                text: l.federationAddIntro,
+                icon: Icons.hub_outlined,
+                onLearnMore: () => showFaiDoc(ctx, 'federation'),
+                learnMoreLabel: l.buttonLearnMore,
+              ),
+              const SizedBox(height: ChainSpace.lg),
+              ChainFieldLabel(
+                label: l.federationNameLabel,
+                help: l.federationNameHelp,
+              ),
+              const SizedBox(height: ChainSpace.xs),
+              TextField(
+                controller: controller,
+                autofocus: true,
+                decoration: const InputDecoration(
+                  hintText: 'satellite-a',
+                  border: OutlineInputBorder(),
+                  isDense: true,
+                ),
+                onSubmitted: (v) => Navigator.pop(ctx, v.trim()),
+              ),
+            ],
           ),
         ),
         actions: [