1.1.6: still image export — PNG / JPG snapshot of the current frame

Adds a "Still image" subgroup under the project column in the export
dialog. Both options render the current playhead frame via the same
drawSceneFrame path used by GIF/APNG, so the still is pixel-identical
to the matching animated frame. JPG fills transparent scenes white;
PNG keeps alpha. Honours the per-export target size for higher-res
poster frames.

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ruwio",
   "private": true,
-  "version": "1.1.5",
+  "version": "1.1.6",
   "type": "module",
   "scripts": {
     "dev": "vite",