Add sharp as explicit dependency for Astro image optimization

pnpm doesn't hoist sharp from astro's optional deps like npm does,
so it needs to be listed directly. Fixes CI build failure.

Author: dannon

website/package.json

@@ -26,6 +26,7 @@
     "mermaid": "^11.12.3",
     "nanostores": "^1.1.0",
     "radix-vue": "^1.9.17",
+    "sharp": "^0.34.5",
     "vue": "^3.5.27",
     "yaml": "^2.8.2"
   },