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/g10k/resources/build.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/bash
+set -e
 
 # Download and extract g10k
 wget -O /app/g10k.zip https://github.com/xorpaul/g10k/releases/download/v${PACKAGE_VERSION}/g10k-v${PACKAGE_VERSION}-linux-amd64.zip
@@ -6,5 +7,8 @@ pushd /app
 unzip /app/g10k.zip
 popd
 
+# Process nfpm.yaml with envsubst
+envsubst < /app/resources/nfpm.yaml > /app/nfpm.yaml
+
 # Build the RPM
-nfpm pkg --config /app/resources/nfpm.yaml --target /app/dist --packager rpm
+nfpm pkg --config /app/nfpm.yaml --target /app/dist --packager rpm