Implement RmlUi GridView support for Objects tab

This implements full dual-mode (Chili + RmlUi) support for GridView,
enabling the Objects tab (Units/Features) and other grid-based UIs
to work in RmlUi mode.

GridView Changes:
- Split initialization into _InitRmlUi() and _InitChili() methods
- Added wrapper methods to hide layoutPanel access from subclasses:
  * ClearChildren(), AddChildItem(), GetChildItem(), Invalidate()
- Updated all public API methods for dual-mode support:
  * GetSelectedItems(), SelectItem(), DeselectAll()
  * StartMultiModify(), EndMultiModify()
  * GetControl() returns placeholder in RmlUi mode
- Created RmlUi-compatible item abstraction in NewItem() and AddItem()
  * Items are simple tables in RmlUi mode, Chili controls in Chili mode
  * Added SetImage() wrapper method to items
- Implemented _UpdateRmlUiGrid() for DOM rendering
- Added _OnRmlUiItemClick() with selection and double-click support
- RmlUi grids use HTML/CSS flexbox layout instead of Chili LayoutPanel

Subclass Updates:
- ObjectDefsPanel: Use wrapper methods instead of direct layoutPanel access
  * Updated FilterItems(), GetObjectDefID(), AddDrawIcon()
  * item.SetImage() instead of item.imgCtrl.file assignment
- AssetView: Made double-click and showPath UI Chili-only
- SavedBrushes: Updated OnBrushImageUpdated() to use item:SetImage()

Editor Integration:
- _FinalizeRmlUi() and _FinalizeRmlUiNew() generate grid container div
- View:OpenEditor() triggers grid update after rendering
- ObjectDefsView stores gridView reference for rendering

CSS:
- Added .grid-container, .grid-item styles with flexbox layout
- Grid items show hover, selected states
- Proper image and label styling within grid items

This maintains full backward compatibility with Chili mode while
enabling the critical Objects tab functionality in RmlUi.

Author: claude

scen_edit/view/asset_view.lua

@@ -25,25 +25,30 @@ function AssetView:init(tbl)
     -- FIXME: Cleanup double click handling hack
     self.__previousDoubleClickTime = Spring.GetTimer()
 
-    self.layoutPanel.MouseDblClick = function(ctrl, x, y, button, mods)
-        if button ~= 1 then
-            return
-        end
-        local cx,cy = ctrl:LocalToClient(x,y)
-        local itemIdx = ctrl:GetItemIndexAt(cx,cy)
+    if self.layoutPanel then
+        -- Chili mode
+        self.layoutPanel.MouseDblClick = function(ctrl, x, y, button, mods)
+            if button ~= 1 then
+                return
+            end
+            local cx,cy = ctrl:LocalToClient(x,y)
+            local itemIdx = ctrl:GetItemIndexAt(cx,cy)
 
-        if itemIdx < 0 then return end
+            if itemIdx < 0 then return end
 
-        local item = self.items[itemIdx]
-        if item == nil then
-            return
-        end
+            local item = self.items[itemIdx]
+            if item == nil then
+                return
+            end
 
-        self:DoubleClickItem(item)
+            self:DoubleClickItem(item)
 
-        return ctrl
+            return ctrl
+        end
     end
-    if self.showPath then
+    -- RmlUi mode: double-click is handled by GridView:_OnRmlUiItemClick
+    if self.showPath and self.layoutPanel then
+        -- Chili mode only
         self.scrollPanel:SetPos(nil, 20)
         self.lblPath = Label:New {
             x = 35,
@@ -113,7 +118,7 @@ function AssetView:DoubleClickItem(item)
 end
 
 function AssetView:SetDir(directory)
-    self.layoutPanel:DeselectAll()
+    self:DeselectAll()
     self.dir = directory
     if self.lblPath then
         self.lblPath:SetCaption(self.dir)

scen_edit/view/editor.lua

@@ -886,8 +886,14 @@ function Editor:_FinalizeRmlUi(children, opts)
         end
     end
 
-    -- Combine buttons and fields
-    self.generatedRml = buttonsHtml .. fieldsHtml
+    -- Generate grid container if editor has a gridView
+    local gridHtml = ''
+    if self.gridView then
+        gridHtml = string.format('<div id="%s" class="grid-container"></div>', self.gridView.gridId)
+    end
+
+    -- Combine buttons, grid, and fields
+    self.generatedRml = buttonsHtml .. gridHtml .. fieldsHtml
 
     -- Mark as hidden by default
     self.hidden = true
@@ -937,8 +943,14 @@ function Editor:_FinalizeRmlUiNew(layout, opts)
         end
     end
 
-    -- Combine buttons and fields
-    self.generatedRml = buttonsHtml .. fieldsHtml
+    -- Generate grid container if editor has a gridView
+    local gridHtml = ''
+    if self.gridView then
+        gridHtml = string.format('<div id="%s" class="grid-container"></div>', self.gridView.gridId)
+    end
+
+    -- Combine buttons, grid, and fields
+    self.generatedRml = buttonsHtml .. gridHtml .. fieldsHtml
 
     -- Mark as hidden by default
     self.hidden = true