Increase VM defaults, restart VM on new workspace, make rebuild writable

bin/qvm-rebuild

@@ -79,7 +79,11 @@ build_base_image() {
     
     # Copy the qcow2 to base image location
     log_info "Copying image to: $QVM_BASE_IMAGE"
+    # Remove existing image first (may be read-only from Nix store copy)
+    rm -f "$QVM_BASE_IMAGE"
     cp -L "$qcow2_path" "$QVM_BASE_IMAGE"
+    # Ensure the new image is writable for future rebuilds
+    chmod 644 "$QVM_BASE_IMAGE"
     
     # Remove the result symlink
     rm -f "$build_result"