feat(ci): parameterize fedora version across pipeline

Add fedora_version to build, package, and publish matrices so the
pipeline can target multiple Fedora releases in parallel. Force the
dist tag via --define to ensure RPMs are stamped correctly regardless
of build host. Update poll-upstream to check all fedora/flavour
combinations before triggering a build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

script/publish-repo.sh

@@ -2,7 +2,8 @@
 set -euo pipefail
 
 RPM_DIR="${1:?usage: $0 <rpm-directory>}"
-REMOTE_DIR="/var/www/rpm/fedora/43/x86_64"
+: "${FEDORA_VERSION:?}"
+REMOTE_DIR="/var/www/rpm/fedora/${FEDORA_VERSION}/x86_64"
 
 # sign each rpm with the imported gpg key
 for rpm in "${RPM_DIR}"/*.rpm; do