Fix hash conversion in NixOS update workflow

- Replace xxd with Python for hex to base64 conversion
- Use standard tools available in GitHub Actions runners
- Should fix hash conversion error in automated workflow

.gitea/workflows/release.yml

@@ -108,8 +108,9 @@ jobs:
           
           # Download tarball to get correct hash
           curl -L -o cm-dashboard.tar.gz "$TARBALL_URL"
+          # Convert sha256 hex to base64 for Nix hash format using Python
           NEW_HASH=$(sha256sum cm-dashboard.tar.gz | cut -d' ' -f1)
-          NIX_HASH="sha256-$(echo -n $NEW_HASH | xxd -r -p | base64)"
+          NIX_HASH="sha256-$(python3 -c "import base64, binascii; print(base64.b64encode(binascii.unhexlify('$NEW_HASH')).decode())")"
           
           # Update the NixOS configuration
           sed -i "s/version = \"v[^\"]*\"/version = \"$VERSION\"/" hosts/common/cm-dashboard.nix