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/landing_page.dart

@@ -0,0 +1,85 @@
+import 'package:flutter/material.dart';
+
+import '../data/repository.dart';
+import '../theme/lawheatmap_theme.dart';
+import '../theme/lawheatmap_tokens.dart';
+import '../widgets/delta_mark.dart';
+import 'shell_page.dart';
+
+/// First-run landing: brand mark, one-line claim, "enter app" CTA.
+/// Mock-mode bypasses Hub connect; the live wire lands in week 1.
+class LandingPage extends StatelessWidget {
+  const LandingPage({super.key, required this.repository});
+
+  final EvaluationRepository repository;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return Scaffold(
+      body: SafeArea(
+        child: Center(
+          child: ConstrainedBox(
+            constraints: const BoxConstraints(maxWidth: 720),
+            child: Padding(
+              padding: const EdgeInsets.symmetric(
+                horizontal: LawHeatmapSpace.xxl,
+                vertical: LawHeatmapSpace.xxxl,
+              ),
+              child: Column(
+                mainAxisAlignment: MainAxisAlignment.center,
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  const DeltaMark(size: 96),
+                  const SizedBox(height: LawHeatmapSpace.xxl),
+                  Text('F∆I Law-Heatmap', style: t.displaySmall),
+                  const SizedBox(height: LawHeatmapSpace.sm),
+                  Text(
+                    'Pflicht-basierte Wirkungsanalyse von Rechtsnormen — '
+                    'auf Ch∆In, mit Quellen-Audit by construction.',
+                    style: t.bodyLarge
+                        ?.copyWith(color: LawHeatmapColors.mute),
+                  ),
+                  const SizedBox(height: LawHeatmapSpace.xxl),
+                  Wrap(
+                    crossAxisAlignment: WrapCrossAlignment.center,
+                    spacing: LawHeatmapSpace.md,
+                    runSpacing: LawHeatmapSpace.sm,
+                    children: [
+                      FilledButton.icon(
+                        onPressed: () {
+                          Navigator.of(context).pushReplacement(
+                            MaterialPageRoute(
+                              builder: (_) =>
+                                  ShellPage(repository: repository),
+                            ),
+                          );
+                        },
+                        icon: const Icon(Icons.east),
+                        label: const Text('App öffnen (Demo-Modus)'),
+                      ),
+                      Text(
+                        'Demo: 5 Pilot-Normen, ohne Hub-Verbindung',
+                        style: t.labelSmall?.copyWith(
+                          color: LawHeatmapColors.mute,
+                        ),
+                      ),
+                    ],
+                  ),
+                  const SizedBox(height: LawHeatmapSpace.xl),
+                  Text(
+                    'v0.1.0  ·  Phase 0  ·  Mock-Modus  ·  '
+                    'Live-Hub-Anbindung folgt in Woche 1',
+                    style: LawHeatmapTheme.mono(
+                      t.labelSmall ?? const TextStyle(),
+                    ).copyWith(color: LawHeatmapColors.mute),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}