fix: add arch=x86_64 to profile, improve abuild key generation in setup

iso/builder/setup-builder.sh

@@ -104,6 +104,24 @@ if [ ! -d /usr/share/aports ]; then
         /usr/share/aports
 fi
 
+# --- abuild signing key (required by mkimage.sh) ---
+if [ ! -f "${HOME}/.abuild/abuild.conf" ]; then
+    echo ""
+    echo "=== generating abuild signing key ==="
+    mkdir -p "${HOME}/.abuild"
+    abuild-keygen -a -n 2>/dev/null || true
+    # abuild-keygen requires doas to install the key system-wide; do it manually
+    PUB=$(ls "${HOME}/.abuild/"*.pub 2>/dev/null | head -1)
+    if [ -n "$PUB" ]; then
+        cp "$PUB" /etc/apk/keys/
+        PRIV="${PUB%.pub}"
+        echo "PACKAGER_PRIVKEY=\"${PRIV}\"" > "${HOME}/.abuild/abuild.conf"
+        echo "abuild key: $PRIV"
+    else
+        echo "WARNING: abuild key generation failed"
+    fi
+fi
+
 echo ""
 echo "=== builder setup complete ==="
 echo "Next: sh iso/builder/build-debug.sh"