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/evidence_sidebar.dart

@@ -0,0 +1,59 @@
+import 'package:flutter/material.dart';
+
+import '../data/models.dart';
+import '../theme/lawheatmap_tokens.dart';
+import 'lawheatmap_card.dart';
+import 'source_chip.dart';
+
+/// Sidebar listing the citable sources behind an evaluation.
+/// Surfaces the methodological audit story: every figure has a
+/// source and an evidence tier.
+class EvidenceSidebar extends StatelessWidget {
+  const EvidenceSidebar({super.key, required this.evaluation});
+
+  final Evaluation evaluation;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return LawHeatmapCard(
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Text('Quellen', style: t.headlineSmall),
+          const SizedBox(height: LawHeatmapSpace.sm),
+          Text(
+            'Jede Zahl trägt die Tier-Stufe ihres schwächsten '
+            'Bestandteils (Regel der niedrigsten Stufe, §6.7).',
+            style: t.labelSmall?.copyWith(color: LawHeatmapColors.mute),
+          ),
+          const SizedBox(height: LawHeatmapSpace.lg),
+          for (final s in evaluation.sources) SourceChip(source: s),
+          const Divider(height: LawHeatmapSpace.xl),
+          Text('Audit-Event', style: t.labelLarge),
+          const SizedBox(height: 4),
+          SelectableText(
+            evaluation.auditEventId,
+            style: t.labelSmall?.copyWith(
+              fontFamily: LawHeatmapTypography.mono,
+              color: LawHeatmapColors.mute,
+            ),
+          ),
+          const SizedBox(height: LawHeatmapSpace.sm),
+          Text(
+            'Quell-SHA-256:',
+            style: t.labelSmall?.copyWith(color: LawHeatmapColors.mute),
+          ),
+          SelectableText(
+            evaluation.norm.sourceSha256,
+            style: t.labelSmall?.copyWith(
+              fontFamily: LawHeatmapTypography.mono,
+              color: LawHeatmapColors.mute,
+              fontSize: 10,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}