Fix RTT texture reference format for RmlUi

Corrected the texture reference format to use RmlUi's proper syntax:
- Changed from `:t{texID}` format to `!{texID}` format
- Use `<texture>` tag instead of `<img>` for GL textures
- Keep `<img>` for regular file paths

RmlUi Texture Reference Format:
- String starting with "!": texture reference (!texID)
  * Use <texture src="!{texID}"> for dynamic GL textures
- Number: OpenGL texture ID from gl.CreateTexture
  * Convert to "!{texID}" format
- Regular string path: standard image file
  * Use <img src="{path}"> as before

This matches Recoil's RmlUi integration where:
- gl.CreateTexture() returns a texID (number)
- Reference it in RML as src="!{texID}"
- The <texture> element displays the GL texture
- Dynamic updates via gl.RenderToTexture work automatically

Now RTT 3D model previews should display correctly in Objects tab.

Author: claude

scen_edit/view/grid_view.lua

@@ -458,19 +458,25 @@ function GridView:_UpdateRmlUiGrid()
             local imagePath = item.image
             -- Handle both file paths (strings) and texture IDs (numbers/tables)
             if type(imagePath) == "string" then
-                -- Regular file path
-                if imagePath:sub(1, 6) == "LuaUI/" then
-                    imagePath = "../../../" .. imagePath
+                -- Check if it's already a texture reference (!texID format)
+                if imagePath:sub(1, 1) == "!" then
+                    -- Already a texture reference from gl.CreateTexture, use <texture> tag
+                    html = html .. string.format('<texture src="%s" class="grid-item-image"/>', imagePath)
+                else
+                    -- Regular file path
+                    if imagePath:sub(1, 6) == "LuaUI/" then
+                        imagePath = "../../../" .. imagePath
+                    end
+                    html = html .. string.format('<img src="%s" class="grid-item-image"/>', imagePath)
                 end
-                html = html .. string.format('<img src="%s" class="grid-item-image"/>', imagePath)
             elseif type(imagePath) == "number" then
-                -- OpenGL texture ID - RmlUi should support this directly
-                -- Format: :t<textureID> for Spring texture references
-                html = html .. string.format('<img src=":t%d" class="grid-item-image"/>', imagePath)
+                -- OpenGL texture ID from gl.CreateTexture
+                -- Format: !<texID> for RmlUi texture references, use <texture> tag
+                html = html .. string.format('<texture src="!%d" class="grid-item-image"/>', imagePath)
             else
                 -- Texture table/object - try to extract ID or convert to string
                 local texId = imagePath.texID or imagePath.id or tostring(imagePath)
-                html = html .. string.format('<img src=":t%s" class="grid-item-image"/>', tostring(texId))
+                html = html .. string.format('<texture src="!%s" class="grid-item-image"/>', tostring(texId))
             end
         end