Add share-as-image to X and Facebook for Q&A cards; v1.0.12

On mobile: Web Share API opens native share sheet with the PNG attached,
letting users pick X, Facebook, Instagram, etc. directly.
On desktop: downloads the image and opens the platform compose window.
"Save image" download button kept alongside the two new share buttons.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "1.0.11",
+  "version": "1.0.12",
   "type": "module",
   "scripts": {
     "dev": "vite",