Tool windows redesign and the Novel Editor workspace

Tool windows:
- Every editor (scenario, scene builder, map, interactive objects,
  lighting, catalog export) is rebuilt on the interface ToolWindow chrome
  and the denser ToolTheme: header with title/close, status bar, Ctrl+S,
  dirty-state confirmation.
- Shared building blocks in src/Common: ToolUi (rows, buttons, sections),
  CollapsibleSection, FilteredList, ModFileSelector, DragHandle and
  BackgroundCanvas (scene background with pan/zoom).
- The map, interactive and light editors draw on canvases
  (MapEditorCanvas, InteractiveEditorCanvas, LightEditorCanvas) instead of
  one Control "handle" node per object; the *Handle classes are removed.
- Scenario editor: tab data model (TabData), automatic graph layout
  (ScenarioGraphLayout), file tree/info/thumbnail panel updates.
- Services: ModFileService (mod file listing and writing),
  SceneBackgroundService; MapFileService/ModResourceService follow.
- Catalog export: per-language name/description editing.
- Locale (en/ru) regrouped under tools/*; unused keys removed.

Novel Editor:
- collections/novel_editor.json: a "game" whose entry scene is an
  authoring workspace over the novel engine and the story content.
- NovelEditorHub (scenes/novel_editor_hub.tscn) lists every installed
  tool through IToolProvider.AddMenuButton; ToolsInitializer registers it
  as the logical scene "novel_editor".

src/ScenarioEditor/ScenarioThumbnailPanel.cs

@@ -9,10 +9,11 @@ namespace Cthangover.Core.UI.Tool.ScenarioEditor
     {
         private HBoxContainer _thumbContainer;
 
-        public ScenarioThumbnailPanel()
-        {
-            _thumbContainer = GetNode<HBoxContainer>("ThumbContainer");
-        }
+        /// <summary>
+        /// Container lookup is lazy: the tscn builder runs the constructor
+        /// before the child nodes exist.
+        /// </summary>
+        private HBoxContainer Thumbs => _thumbContainer ??= GetNode<HBoxContainer>("ThumbContainer");
 
         /// <summary>Loads the background thumbnails referenced by the given scenario text (missing ones render as placeholders).</summary>
         public void Load(string text)
@@ -26,7 +27,7 @@ namespace Cthangover.Core.UI.Tool.ScenarioEditor
 
             if (refs.BackgroundRefs.Count == 0)
             {
-                _thumbContainer.AddChild(new Label
+                Thumbs.AddChild(new Label
                 {
                     Text = TranslationServer.Translate("tools/scenario_editor/no_backgrounds")
                 });
@@ -39,7 +40,7 @@ namespace Cthangover.Core.UI.Tool.ScenarioEditor
 
                 if (tex != null)
                 {
-                    _thumbContainer.AddChild(new TextureRect
+                    Thumbs.AddChild(new TextureRect
                     {
                         Texture = tex,
                         ExpandMode = TextureRect.ExpandModeEnum.IgnoreSize,
@@ -50,10 +51,10 @@ namespace Cthangover.Core.UI.Tool.ScenarioEditor
                 }
                 else
                 {
-                    _thumbContainer.AddChild(new Label
+                    Thumbs.AddChild(new Label
                     {
                         Text = $"[? {id}]",
-                        TooltipText = $"Not found: {id}"
+                        TooltipText = string.Format(TranslationServer.Translate("tools/scenario_editor/bg_missing"), id)
                     });
                 }
             }
@@ -62,7 +63,7 @@ namespace Cthangover.Core.UI.Tool.ScenarioEditor
         /// <summary>Removes every thumbnail from the row.</summary>
         public new void Clear()
         {
-            foreach (var c in _thumbContainer.GetChildren())
+            foreach (var c in Thumbs.GetChildren())
                 c.QueueFree();
         }
     }