- .gitea/workflows/build-deploy.yml: trigger on [main, staging, devel];
build step picks publishconf.py (main) / stagingconf.py (staging) /
bare pelicanconf.py (devel, same as a plain local build); deploy
step already had prod-vs-test branching, updated its ref check from
master to main to match the repo's renamed default branch.
- stagingconf.py: new, prod-like preview config (feeds, absolute URLs)
pointed at the internal dev webserver instead of the real domain.
- pelicanconf.py: SITEURL set to the dev webserver address (was ''),
used by both stagingconf.py and bare devel builds.
