feat(studio): module sheet permissions get a help icon → security doc

When operators open a module's detail sheet from the Store,
the Permissions section now grows a small help icon next to
the section header. Tapping it opens the bundled security.md
explainer in the existing bottom-sheet reader, the same
in-app help system Approvals + Audit + Doctor already use.

Closes the zero-learning-curve gap: every operator-facing
declaration of permissions ('net: api.openai.com', 'fs.read:
…') now has a clickable affordance to learn what those
permission categories mean and how the sandbox enforces them.

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

lib/widgets/fai_module_sheet.dart

@@ -8,6 +8,7 @@ import 'package:flutter/material.dart';
 import '../data/error_presentation.dart';
 import '../data/hub.dart';
 import '../l10n/app_localizations.dart';
+import '../pages/welcome.dart' show showFaiDoc;
 import '../theme/theme.dart';
 import '../theme/tokens.dart';
 import 'fai_pill.dart';
@@ -239,7 +240,24 @@ class _Body extends StatelessWidget {
               .toList(),
         ),
         const SizedBox(height: FaiSpace.xl),
-        _SectionHeader(l.moduleSheetPermissions),
+        Row(
+          children: [
+            _SectionHeader(l.moduleSheetPermissions),
+            const SizedBox(width: 4),
+            InkWell(
+              onTap: () => showFaiDoc(context, 'security'),
+              borderRadius: BorderRadius.circular(8),
+              child: Padding(
+                padding: const EdgeInsets.all(4),
+                child: Icon(
+                  Icons.help_outline,
+                  size: 14,
+                  color: theme.colorScheme.onSurfaceVariant,
+                ),
+              ),
+            ),
+          ],
+        ),
         const SizedBox(height: FaiSpace.sm),
         if (detail.permissions.isEmpty)
           Text(