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/nzbget/resources/build.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/bash
 
+set -e
+
 # Download the pre-built RPM from GitHub releases
-curl -o /app/dist/nzbget-${PACKAGE_VERSION}-${PACKAGE_RELEASE}.x86_64.rpm \
+curl -L -o /app/dist/nzbget-${PACKAGE_VERSION}-${PACKAGE_RELEASE}.x86_64.rpm \
   https://github.com/nzbgetcom/nzbget/releases/download/v$PACKAGE_VERSION/nzbget-${PACKAGE_VERSION}-${PACKAGE_RELEASE}.x86_64.rpm