Fix arm64 Docker build crash (QEMU illegal instruction); v1.1.13

Run npm ci on the native build platform using --platform=\$BUILDPLATFORM in a
deps stage, then copy node_modules to the runtime image. Avoids running Node.js
under QEMU emulation, which crashes with SIGILL on arm64 cross-builds.

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "1.1.12",
+  "version": "1.1.13",
   "type": "module",
   "scripts": {
     "dev": "vite",