feat: guided setup — persona re-audit fixes (grade-1 round)

- Regulated path finishes without a terminal: the signed-source
  state offers 'Add a signed source…' (stores dialog with pin-a-key)
  plus the per-module install buttons and a plain-language hint why
  pinning the publisher's key matters — instead of a hint with no
  affordance.
- Apply warnings (e.g. the empty-trusted-publishers caveat) surface
  selectable in the done state instead of being swallowed.
- Truthful preview: new lines state which machine is being set up
  (server/container targets configure THIS machine), that regulated
  profiles always get the hash-chained audit log (even with WORM
  off), and that the curated reading list is stored with the setup
  record.
- Language pass: onboarding checklist in Sie-form + 'System-KI'
  (was du-form + 'System-AI'), 'Audit-Sperre' jargon replaced,
  answers file moved to a private per-dialog temp dir.
- Screenshot harness: GUIDE_SHOTS_THEME=light for light-parity
  proof runs.

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

integration_test/guide_shots_test.dart

@@ -72,6 +72,13 @@ Future<void> _pumpUntil(
 String get _outDir =>
     Platform.environment['GUIDE_SHOTS_OUT'] ?? 'build/guide-shots';
 
+/// Guide images ship dark; GUIDE_SHOTS_THEME=light exists for the
+/// light-parity proof runs (release gate: both themes must hold).
+ThemeModeValue get _theme =>
+    Platform.environment['GUIDE_SHOTS_THEME'] == 'light'
+    ? ThemeModeValue.light
+    : ThemeModeValue.dark;
+
 /// Rasterize the app's RepaintBoundary into `<outDir>/<name>.png`.
 Future<void> _shot(WidgetTester tester, String name) async {
   // Two extra frames so ripples/route transitions settle visually.
@@ -179,9 +186,9 @@ void main() {
     await tester.pumpWidget(
       RepaintBoundary(
         key: _shotKey,
-        child: const StudioApp(
-          initialThemeMode: ThemeModeValue.dark,
-          initialLocale: Locale('de'),
+        child: StudioApp(
+          initialThemeMode: _theme,
+          initialLocale: const Locale('de'),
         ),
       ),
     );