feat(studio): swap built-in flow editor for fai_studio_flow_editor package (v0.51.0)

The flow editor was internal to Studio (lib/pages/flow_editor.dart).
Per Stefan's review feedback ("austauschbar wäre schöner"),
extract it into its own Forgejo repo so the host can swap
the implementation without touching Studio.

New repo: https://git.flemming.ai/fai/studio-flow-editor

Studio's pubspec.yaml now references the package by git URL:

  dependencies:
    fai_studio_flow_editor:
      git:
        url: https://git.flemming.ai/fai/studio-flow-editor
        ref: main

To swap the editor:
  1. Fork (or write a new) fai/studio-flow-editor.
  2. Keep the FlowEditorPage(initialFlowName, locale, onRun)
     constructor signature — the stable host contract.
  3. Point the pubspec at your fork.
  4. Rebuild Studio.

Adapter pattern: _FlowEditorAdapter in main.dart resolves the
package's runtime dependencies (locale via Localizations,
onRun via HubService) from the BuildContext, then constructs
the package's FlowEditorPage. Same pattern in flows.dart for
the pencil → editor route push, so a future operator-side
locale switch propagates correctly.

The package brings its own copies of FaiSpace tokens, minimal
FaiEmptyState/FaiErrorBox widgets, and an inline EN+DE l10n
table — accepting a small amount of visual drift in exchange
for true package independence. flutter_code_editor +
highlight move from Studio's pubspec to the package's.

Deleted:
  lib/pages/flow_editor.dart  → package's lib/src/flow_editor_page.dart
  test/flow_editor_test.dart  → package's test/ (next commit there)

Bumped:
  pubspec.yaml version 0.50.0 → 0.51.0
  main.dart kStudioVersion 0.50.0 → 0.51.0
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/main.dart

@@ -5,8 +5,8 @@
 
 import 'dart:async';
 
+import 'package:fai_studio_flow_editor/fai_studio_flow_editor.dart';
 import 'package:flutter/material.dart';
-
 import 'package:flutter/services.dart';
 
 import 'data/hub.dart';
@@ -16,7 +16,6 @@ import 'l10n/app_localizations.dart';
 import 'pages/approvals.dart';
 import 'pages/audit.dart';
 import 'pages/doctor.dart';
-import 'pages/flow_editor.dart';
 import 'pages/flows.dart';
 import 'pages/store.dart';
 import 'pages/welcome.dart';
@@ -28,7 +27,7 @@ import 'widgets/widgets.dart';
 /// Studio's own build version. Bump on every UI commit so the
 /// running app self-identifies — visible in the sidebar header
 /// and quick-glance proof that you're seeing the current build.
-const String kStudioVersion = '0.50.0';
+const String kStudioVersion = '0.51.0';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -239,7 +238,7 @@ class _StudioShellState extends State<StudioShell> {
       id: 'flow-editor',
       icon: Icons.code_outlined,
       selectedIcon: Icons.code,
-      page: FlowEditorPage(),
+      page: _FlowEditorAdapter(),
     ),
     _NavPage(
       id: 'audit',
@@ -1062,3 +1061,23 @@ class _LanguageToggle extends StatelessWidget {
     );
   }
 }
+
+/// Adapter that resolves the swappable FlowEditorPage's
+/// runtime dependencies (locale, hub onRun callback) from
+/// Studio's BuildContext. The _NavPage destination list
+/// holds widgets as const-ish, so the adapter sits in
+/// between to grab live data.
+class _FlowEditorAdapter extends StatelessWidget {
+  const _FlowEditorAdapter();
+
+  @override
+  Widget build(BuildContext context) {
+    final lang = Localizations.localeOf(context).languageCode;
+    return FlowEditorPage(
+      locale: lang == 'de' ? FlowEditorLocale.de : FlowEditorLocale.en,
+      onRun: (name) async =>
+          (await HubService.instance.runSavedFlow(name: name))
+              .cast<String, Object>(),
+    );
+  }
+}