feat(setup): first-run gate, hub-first preview, honest wording — setup before the app

Stefan's live findings, all four addressed at the root:

- 'In 3 Fragen loslegen' read like ad copy → the entry is now plainly
  'Einrichtung starten' / 'Start setup'.
- The setup button sat permanently on the Welcome page of a running
  app ('setup after the app runs is backwards' — reported twice). A
  fresh install now starts INSIDE the setup: SetupGateScreen hosts
  the wizard embedded as the page (new embedded/onFinished modes on
  GuidedSetupDialog), with an explicit 'Später einrichten' skip.
  Welcome loses the setup button entirely and stays a calm intro.
- Re-running the setup later lives in Settings → General ('Run setup
  again…'), the single post-first-run home.
- 'You must grant access first and only then see what will be done':
  the preview used to spawn the chain CLI, whose first run could pop
  the macOS permission prompt BEFORE the plan was ever shown. The
  preview now calls the new PlanSetup RPC over the live hub
  connection (no subprocess, nothing granted); the CLI remains only
  a fallback when no hub is reachable — and applying stays the
  explicit, separate step.

Widget tests: gate hosts the wizard + skip/cancel leave it; CLI-path
tests drive the fallback through the new hub-preview test seam.
Suite 76 green, analyze clean.

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

lib/pages/setup_gate.dart

@@ -0,0 +1,81 @@
+// First-run gate. On a fresh install (no ~/.chain/config.yaml, no
+// setup-plan.yaml) the app opens INTO the setup instead of showing
+// the full shell with a wizard dialog on top — setup before the
+// app, not after. The guided-setup wizard renders embedded as the
+// page content; "Später einrichten" skips into the app for this
+// run (the gate returns on the next launch as long as nothing is
+// configured — the wizard IS the onboarding until then).
+
+import 'package:flutter/material.dart';
+
+import '../l10n/app_localizations.dart';
+import '../theme/tokens.dart';
+import '../widgets/guided_setup_dialog.dart';
+
+class SetupGateScreen extends StatelessWidget {
+  /// Called when the operator finishes the setup or skips — the
+  /// app swaps this screen for the normal shell.
+  final VoidCallback onDone;
+
+  const SetupGateScreen({super.key, required this.onDone});
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Scaffold(
+      backgroundColor: theme.scaffoldBackgroundColor,
+      body: Center(
+        child: SingleChildScrollView(
+          padding: const EdgeInsets.all(ChainSpace.xl),
+          child: ConstrainedBox(
+            constraints: const BoxConstraints(maxWidth: 560),
+            child: Column(
+              mainAxisSize: MainAxisSize.min,
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  'Ch∆In Studio',
+                  style: theme.textTheme.titleMedium?.copyWith(
+                    color: theme.colorScheme.primary,
+                    fontWeight: FontWeight.w700,
+                  ),
+                ),
+                const SizedBox(height: ChainSpace.xs),
+                Text(
+                  l.setupGateIntro,
+                  style: theme.textTheme.bodyMedium?.copyWith(
+                    color: theme.colorScheme.onSurfaceVariant,
+                  ),
+                ),
+                const SizedBox(height: ChainSpace.lg),
+                Container(
+                  padding: const EdgeInsets.all(ChainSpace.xl),
+                  decoration: BoxDecoration(
+                    color: theme.colorScheme.surfaceContainerLow,
+                    borderRadius: BorderRadius.circular(ChainRadius.md),
+                    border: Border.all(
+                      color: theme.colorScheme.outlineVariant,
+                    ),
+                  ),
+                  child: GuidedSetupDialog(
+                    embedded: true,
+                    onFinished: onDone,
+                  ),
+                ),
+                const SizedBox(height: ChainSpace.sm),
+                Align(
+                  alignment: Alignment.centerRight,
+                  child: TextButton(
+                    onPressed: onDone,
+                    child: Text(l.setupGateSkip),
+                  ),
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}