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/widgets/demo_banner.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+
+import '../theme/lawheatmap_tokens.dart';
+
+/// Permanent banner shown above all data screens in mock mode.
+/// Carries the political-defensibility caveat: this is demo data,
+/// not peer-reviewed, not Juristen-approved.
+class DemoBanner extends StatelessWidget {
+  const DemoBanner({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.symmetric(
+        horizontal: LawHeatmapSpace.lg,
+        vertical: LawHeatmapSpace.sm,
+      ),
+      decoration: BoxDecoration(
+        color: LawHeatmapColors.tierT4.withValues(alpha: 0.12),
+        border: Border(
+          bottom: BorderSide(
+            color: LawHeatmapColors.tierT4.withValues(alpha: 0.55),
+          ),
+        ),
+      ),
+      child: Row(
+        children: [
+          const Icon(Icons.science_outlined,
+              size: 18, color: LawHeatmapColors.tierT4),
+          const SizedBox(width: LawHeatmapSpace.sm),
+          Expanded(
+            child: Text(
+              'Demo-Daten — Phase 0, ohne Verbands-Erhebung. '
+              'Keine Juristen-Approval, keine Beirats-Validierung. '
+              'Alle Werte tragen Tier T4, bis T1/T2-Pipeline läuft.',
+              style: t.labelSmall?.copyWith(
+                color: LawHeatmapColors.tierT4,
+              ),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}