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

.gitea/workflows/build.yaml

@@ -20,7 +20,7 @@ jobs:
         env:
           VAULT_ROLE_ID: ${{ secrets.RPMBUILDER_VAULT_ROLEID }}
         run: |
-          make all DISTRO=el/8
+          ./tools/build build-all --distro almalinux/el8
 
       - name: Show RPMs
         run: |
@@ -46,7 +46,7 @@ jobs:
         env:
           VAULT_ROLE_ID: ${{ secrets.RPMBUILDER_VAULT_ROLEID }}
         run: |
-          make all DISTRO=el/9
+          ./tools/build build-all --distro almalinux/el9
 
       - name: Show RPMs
         run: |