fix: also allow sharp build script (transitive via wrangler→miniflare)

CI uses pnpm install --frozen-lockfile which enforces strictDepBuilds;
sharp is a transitive dep with postinstall, so it must be explicitly
allowed too. Local pnpm install --force masked this previously.

pnpm-workspace.yaml

@@ -1,3 +1,4 @@
 allowBuilds:
   esbuild: true
+  sharp: true
   workerd: true