feat: initial F∆I Law-Heatmap Phase 0 scaffold

First end-to-end-buildable cut of the pflicht-/graph-basierte
Wirkungsanalyse von Rechtsnormen, running on Ch∆In. Demo runs
without external dependencies and without a hub connection so
the methodology + UI stack can be reviewed before any Verbands-
Kooperation or Beirats-Validierung kicks in.

Tree layout

  MACHBARKEITSSTUDIE.md       v0.3 — pflicht-basierte Methodik,
                              4-Tier-Evidenz, 8 law*-Module
                              auf Ch∆In statt der alten F∆I-
                              Plattform.
  RUN.md                      one-page how-to-run.
  flows/durchstich-gewo-14.yaml
                              vertical Phase-0 flow: pull →
                              normalize → duties → citations →
                              cohort → skm → frust → benefit →
                              attribution → system.approval.
  app/                        Flutter macOS client, design
                              language pulled from fai_web
                              (ink #08090A, paper #F4F3EF,
                              petrol signal #2E8F9E). Mock
                              repository ships five fixture
                              norms with real source URLs and a
                              permanent T4 demo-banner so no
                              figure can be mistaken for a
                              validated one.

Module repos (separate, see chain-modules*/):

  text-akoma-normalize, text-deontic-extract, graph-citation-
  extract, text-readability-score, stats-cohort-size, graph-
  shapley-attribution, econ-skm-score, law-benefit-score.

What runs today

  - flutter analyze: 0 issues
  - flutter test: 2/2 (landing + nav-to-shell smoke)
  - flutter build macos (via app/build-macos.sh) and ad-hoc
    codesign, app launches and the Dart VM service comes up
  - native cargo test green on every module
  - cargo build --release --target wasm32-wasip2 produces a
    130 KiB artefact for text-akoma-normalize

What is deliberately mock / stub

  - gRPC wire from the client to a chain serve hub (Repository
    abstraction is in place; live impl is the next step)
  - NKR Bürokratiekosten-Datenbank ingestion (for the canonical
    h-Werte that close out the Engpass per Studie §6.7)
  - DESTATIS GENESIS-API adapter for stats.cohort_size

License: Apache-2.0. Author/contact in MACHBARKEITSSTUDIE.md.
Signed-off-by: flemming-it <sf@flemming.it>

app/lib/pages/hub_status_page.dart

@@ -0,0 +1,90 @@
+import 'package:flutter/material.dart';
+
+import '../data/repository.dart';
+import '../theme/lawheatmap_tokens.dart';
+import '../widgets/lawheatmap_card.dart';
+
+class HubStatusPage extends StatelessWidget {
+  const HubStatusPage({super.key, required this.repository});
+
+  final EvaluationRepository repository;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return SingleChildScrollView(
+      padding: const EdgeInsets.all(LawHeatmapSpace.xl),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Text('Ch∆In Hub', style: t.displaySmall),
+          const SizedBox(height: LawHeatmapSpace.xs),
+          Text(
+            'Status der Verbindung zum lokalen Hub und des Audit-Logs.',
+            style: t.bodyLarge?.copyWith(color: LawHeatmapColors.mute),
+          ),
+          const SizedBox(height: LawHeatmapSpace.lg),
+          LawHeatmapCard(
+            accent: true,
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                _row('Modus', repository.mode.toUpperCase(), t),
+                _row('Quelle', repository.hubLabel, t),
+                _row('gRPC-Endpunkt', '— (Phase-0-Stub)', t),
+                _row('Audit-DB', '~/.chain/chain.db (geplant)', t),
+                _row('Hash-Tag', 'CHAIN-EVENT-V3', t),
+              ],
+            ),
+          ),
+          const SizedBox(height: LawHeatmapSpace.lg),
+          LawHeatmapCard(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text('Geplante Live-Anbindung', style: t.headlineSmall),
+                const SizedBox(height: LawHeatmapSpace.sm),
+                Text(
+                  '1. `chain serve` startet lokal auf Port 50051.\n'
+                  '2. Diese App liest `~/.chain/hub-auth-token` und '
+                  'verbindet via gRPC.\n'
+                  '3. Capability `text.akoma_normalize@^0` muss '
+                  'installiert sein (`chain install text.akoma_normalize`).\n'
+                  '4. Pilot-Flow `flows/durchstich-gewo-14.yaml` läuft '
+                  'gegen GewO §14.\n'
+                  '5. Jedes step.completed-Event landet im Audit-Log; '
+                  'die Repository-Implementierung tauscht von MockRepository '
+                  'auf HubRepository (gleiches Interface, kein UI-Wechsel).',
+                  style: t.bodyLarge?.copyWith(
+                    height: 1.6,
+                  ),
+                ),
+              ],
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+
+  Widget _row(String label, String value, TextTheme t) {
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 4),
+      child: Row(
+        children: [
+          SizedBox(
+            width: 160,
+            child: Text(label,
+                style: t.labelLarge
+                    ?.copyWith(color: LawHeatmapColors.mute)),
+          ),
+          Expanded(
+            child: Text(value,
+                style: t.bodyLarge
+                    ?.copyWith(fontFamily: LawHeatmapTypography.mono)),
+          ),
+        ],
+      ),
+    );
+  }
+}