Remove QEMU, build linux/arm64 natively on ARM runner; v2.0.48

Runner is on the ARM server so linux/arm64 builds natively — no QEMU
or cross-compilation needed. Drop setup-qemu-action and amd64 platform.

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.0.46",
+  "version": "2.0.48",
   "type": "module",
   "scripts": {
     "dev": "vite",