feat: F∆I Studio MVP scaffold (Tier-2 desktop GUI)

Initial scaffold for the F∆I Platform Tier-2 generic GUI client.
Flutter Desktop (macOS, Linux, Windows). Three MVP pages with
mock data, sharing one navigation shell:

- Modules — installed modules with capabilities, declared
  permissions and required services.
- Audit — event-stream view with type filter and tone-coded
  rows (started / completed / failed).
- Approvals — pending system.approval@^0 reviews with prompt,
  payload preview, and approve/reject buttons.

Live gRPC connection arrives in the next iteration via
fai_dart_sdk (sibling repo, currently a typed stub).

Future Forgejo path: fai/studio. Local layout matches existing
fai_platform/ convention.

Background: see docs/architecture/client.md in the platform
repo. The tier-2 client was previously called "Stage" — renamed
to "Studio" on 2026-05-05 to avoid confusion with
"staging environment".

flutter analyze: clean. flutter test: 2/2.

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

lib/pages/modules.dart

@@ -0,0 +1,133 @@
+import 'package:flutter/material.dart';
+
+import '../data/mock.dart';
+
+class ModulesPage extends StatelessWidget {
+  const ModulesPage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Installed Modules'),
+        centerTitle: false,
+      ),
+      body: ListView.separated(
+        padding: const EdgeInsets.all(24),
+        itemCount: mockModules.length,
+        separatorBuilder: (_, _) => const SizedBox(height: 12),
+        itemBuilder: (context, i) {
+          final m = mockModules[i];
+          return Card(
+            elevation: 0,
+            shape: RoundedRectangleBorder(
+              borderRadius: BorderRadius.circular(12),
+              side: BorderSide(color: theme.colorScheme.outlineVariant),
+            ),
+            child: Padding(
+              padding: const EdgeInsets.all(16),
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Row(
+                    children: [
+                      Text(
+                        m.name,
+                        style: theme.textTheme.titleMedium?.copyWith(
+                          fontWeight: FontWeight.w600,
+                        ),
+                      ),
+                      const SizedBox(width: 8),
+                      Container(
+                        padding: const EdgeInsets.symmetric(
+                          horizontal: 8,
+                          vertical: 2,
+                        ),
+                        decoration: BoxDecoration(
+                          color: theme.colorScheme.secondaryContainer,
+                          borderRadius: BorderRadius.circular(4),
+                        ),
+                        child: Text(
+                          'v${m.version}',
+                          style: theme.textTheme.bodySmall?.copyWith(
+                            color: theme.colorScheme.onSecondaryContainer,
+                          ),
+                        ),
+                      ),
+                    ],
+                  ),
+                  const SizedBox(height: 8),
+                  _Row(label: 'Capabilities', items: m.capabilities),
+                  if (m.permissions.isNotEmpty) ...[
+                    const SizedBox(height: 6),
+                    _Row(label: 'Permissions', items: m.permissions),
+                  ],
+                  if (m.requiresServices.isNotEmpty) ...[
+                    const SizedBox(height: 6),
+                    _Row(
+                      label: 'Requires services',
+                      items: m.requiresServices,
+                    ),
+                  ],
+                ],
+              ),
+            ),
+          );
+        },
+      ),
+    );
+  }
+}
+
+class _Row extends StatelessWidget {
+  final String label;
+  final List<String> items;
+
+  const _Row({required this.label, required this.items});
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Row(
+      crossAxisAlignment: CrossAxisAlignment.start,
+      children: [
+        SizedBox(
+          width: 140,
+          child: Text(
+            label,
+            style: theme.textTheme.bodySmall?.copyWith(
+              color: theme.colorScheme.onSurfaceVariant,
+            ),
+          ),
+        ),
+        Expanded(
+          child: Wrap(
+            spacing: 6,
+            runSpacing: 6,
+            children: items
+                .map(
+                  (s) => Container(
+                    padding: const EdgeInsets.symmetric(
+                      horizontal: 8,
+                      vertical: 3,
+                    ),
+                    decoration: BoxDecoration(
+                      color: theme.colorScheme.surfaceContainerHighest,
+                      borderRadius: BorderRadius.circular(4),
+                    ),
+                    child: Text(
+                      s,
+                      style: theme.textTheme.bodySmall?.copyWith(
+                        fontFamily: 'monospace',
+                      ),
+                    ),
+                  ),
+                )
+                .toList(),
+          ),
+        ),
+      ],
+    );
+  }
+}