Add button compatibility layer for RmlUi editors

Buttons (TabbedPanelButton and Button:New) now work automagically in both
Chili and RmlUi modes through the compatibility layer.

Changes:
- Add button compatibility layer in rmlui_field_compat.lua
  - RmlUiTabbedPanelButton: Action buttons (Add, Set, Smooth, etc.)
  - RmlUiButton: Regular buttons added via AddControl()
  - Override TabbedPanelButton(), Button.New() to create RmlUi buttons
  - Buttons store OnClick handlers, captions, images, tooltips
  - SetPressedState() updates button CSS class when pressed

- Update Editor:_FinalizeRmlUi() to process buttons from children
  - Extract action buttons and regular buttons from children array
  - Generate HTML for action buttons panel at top of editor
  - Generate HTML for regular buttons within fields section
  - Store buttons for event binding

- Update View:BindFieldEvents() to bind button click events
  - Bind action button clicks to their OnClick handlers
  - Bind regular button clicks to their OnClick handlers
  - Use CallListeners() to invoke handlers

- Add CSS styling for action buttons
  - .action-buttons-panel: Horizontal button strip at editor top
  - .action-button: 70x70dp buttons with icon + label
  - .action-button.pressed: Green highlight when active
  - .action-button-icon and .action-button-label styling

- Delete unused RmlUi editor files
  - rmlui_editor_base.lua: Separate editor approach not used
  - rmlui_components.lua: Empty editor stubs not used
  - Keep rmlui_component.lua (used by picker windows)

All existing editors (heightmap, metal, grass, texture, etc.) now have
their action buttons working in RmlUi mode without any code changes.

Author: claude

scen_edit/view/editor.lua

@@ -118,7 +118,7 @@ function Editor:Finalize(children, opts)
 
     -- In RmlUi mode, generate RML from fields instead of creating Chili controls
     if SB.view and SB.view.useRmlUi then
-        self:_FinalizeRmlUi(opts)
+        self:_FinalizeRmlUi(children, opts)
         self.__initializing = false
         return
     end
@@ -725,25 +725,59 @@ end
 SB.IncludeDir(Path.Join(SB.DIRS.SRC, 'view/fields'))
 
 -- RmlUi-specific finalization
-function Editor:_FinalizeRmlUi(opts)
-    -- Generate RML for all fields
-    local html = ''
+function Editor:_FinalizeRmlUi(children, opts)
+    children = children or {}
+    opts = opts or {}
+
+    -- Extract action buttons from children (TabbedPanelButton instances)
+    self.actionButtons = {}
+    self.regularButtons = {}
+
+    for _, child in ipairs(children) do
+        if child and type(child) == "table" then
+            -- Check if it's an RmlUi button
+            if child.GenerateRml and child.OnClick then
+                if child.id and child.id:match("^action%-btn%-") then
+                    table.insert(self.actionButtons, child)
+                elseif child.id and child.id:match("^btn%-") then
+                    table.insert(self.regularButtons, child)
+                end
+            end
+        end
+    end
 
+    -- Generate RML for action buttons (placed at top)
+    local buttonsHtml = ''
+    if #self.actionButtons > 0 then
+        buttonsHtml = '<div class="action-buttons-panel">'
+        for _, button in ipairs(self.actionButtons) do
+            buttonsHtml = buttonsHtml .. button:GenerateRml()
+        end
+        buttonsHtml = buttonsHtml .. '</div>'
+    end
+
+    -- Generate RML for all fields
+    local fieldsHtml = ''
     for _, fieldName in ipairs(self.fieldOrder) do
         local field = self.fields[fieldName]
         -- Skip fields that are children of GroupFields (they're rendered by the group)
         if field and not field._isGroupChild then
             if field.GenerateRml then
-                html = html .. field:GenerateRml()
+                fieldsHtml = fieldsHtml .. field:GenerateRml()
             else
-                -- Fallback for fields without GenerateRml (like separators/controls)
-                html = html .. '<div class="field-separator"></div>'
+                -- Check if it's a control with a button
+                if field.ctrl and field.ctrl.GenerateRml then
+                    fieldsHtml = fieldsHtml .. field.ctrl:GenerateRml()
+                else
+                    -- Fallback for other controls
+                    fieldsHtml = fieldsHtml .. '<div class="field-separator"></div>'
+                end
             end
         end
     end
 
-    -- Store the generated RML for later use
-    self.generatedRml = html
+    -- Combine buttons and fields
+    self.generatedRml = buttonsHtml .. fieldsHtml
 
     -- Mark as hidden by default
     self.hidden = true

scen_edit/view/rcss/springboard.rcss

@@ -202,12 +202,69 @@ body#springboard {
     border: 1dp #2a5f8f;
     padding: 5dp 10dp;
     cursor: pointer;
+    margin-bottom: 10dp;
 }
 
 .field-button:hover {
     background-color: #4a8ecf;
 }
 
+/* Action buttons panel at top of editor */
+.action-buttons-panel {
+    display: flex;
+    flex-direction: row;
+    gap: 0dp;
+    margin-bottom: 15dp;
+    padding: 5dp;
+    background-color: #2a2a2a;
+    border-bottom: 1dp #555555;
+}
+
+.action-button {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    width: 70dp;
+    height: 70dp;
+    background-color: #3a3a3a;
+    border: 1dp #555555;
+    padding: 5dp;
+    cursor: pointer;
+    margin-right: 0dp;
+}
+
+.action-button:hover {
+    background-color: #4a4a4a;
+    border-color: #777777;
+}
+
+.action-button.pressed {
+    background-color: #2a5f2a;
+    border-color: #3a7f3a;
+}
+
+.action-button-icon {
+    width: 35dp;
+    height: 35dp;
+    margin-bottom: 3dp;
+}
+
+.action-button.pressed .action-button-icon {
+    decorator: image;
+    image-color: #00ff00;
+}
+
+.action-button-label {
+    font-size: 11dp;
+    color: #ffffff;
+    text-align: center;
+}
+
+.action-button.pressed .action-button-label {
+    color: #00ff00;
+}
+
 .field-separator {
     height: 1dp;
     background-color: #555555;