fix: correct $VERSION reference in build-iso.sh, fix QEMU networking

- src/build-iso.sh: Replace undefined $VERSION with correct filename.
  The success check referenced $PROJECT_NAME-v$VERSION.iso but $VERSION
  was never defined, causing the build to always report failure.
- scripts/validate-iso.sh: Replace deprecated `-net nic -net user` with
  modern `-nic user` QEMU networking syntax.

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

scripts/validate-iso.sh

@@ -226,7 +226,7 @@ phase2_boot_test() {
         -drive file="$VM_DISK",format=qcow2,if=virtio \
         -cdrom "$ISO_PATH" \
         -boot d \
-        -net nic -net user \
+        -nic user \
         -serial file:"$SERIAL_LOG" \
         -display none \
         -no-reboot \

src/build-iso.sh

@@ -185,11 +185,11 @@ fi
   echo ""
   echo "=== BUILD COMPLETION CHECK ==="
 
-  if [ -f "output/$PROJECT_NAME-v$VERSION.iso" ]; then
+  if [ -f "output/$PROJECT_NAME.iso" ]; then
     echo "PASS: BUILD SUCCESSFUL!"
-    echo "PASS: ISO created: $PROJECT_NAME-v$VERSION.iso"
-    echo "PASS: Size: $(du -h "output/$PROJECT_NAME-v$VERSION.iso" | cut -f1)"
-    echo "PASS: SHA256: $(cut -d' ' -f1 < "output/$PROJECT_NAME-v$VERSION.sha256")"
+    echo "PASS: ISO created: $PROJECT_NAME.iso"
+    echo "PASS: Size: $(du -h "output/$PROJECT_NAME.iso" | cut -f1)"
+    echo "PASS: SHA256: $(cut -d' ' -f1 < "output/$PROJECT_NAME.sha256")"
     echo "All operations performed in Docker container - NO host modifications"
     return 0
   else