refactor: modernise RPM builder with Python tooling v2

- Migrate from legacy shell-based build system to modern Python tooling
- Update all metadata.yaml files to new schema with per-distro builds
- Standardise build scripts with curl -L, envsubst, and error handling
- Convert nfpm.yaml templates to use environment variable substitution
- Update Dockerfile to accept all package metadata as build arguments
- Modernise Makefile to use new Python build tool commands
- Update CI workflow to use tools/build instead of make

rpms/jsonnet/resources/build.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/bash
+set -e
 
 # Install dependencies and Go 1.24
 dnf install -y wget git make
@@ -16,5 +17,8 @@ go version
 GOBIN=/app go install github.com/google/go-jsonnet/cmd/jsonnet@v${PACKAGE_VERSION}
 GOBIN=/app go install github.com/google/go-jsonnet/cmd/jsonnetfmt@v${PACKAGE_VERSION}
 
+# Process nfpm.yaml with envsubst
+envsubst < /app/resources/nfpm.yaml > /app/nfpm.yaml
+
 # Build RPM package
-nfpm pkg --config /app/resources/nfpm.yaml --target /app/dist --packager rpm
+nfpm pkg --config /app/nfpm.yaml --target /app/dist --packager rpm