Release setup: tarballs, Gitea workflow, apt registry

make dist builds tarballs for linux/amd64 and linux/arm64. A pushed v*
tag runs .gitea/workflows/release.yml, which checks the tag against
VERSION and the CHANGELOG, tests, builds the tarballs and the .debs
(amd64, arm64) and publishes them with scripts/gitea-release.sh: a Gitea
release, and the .debs in the Debian registry (stable, or testing for a
release candidate). As in Housecarl and Steward; no cli-dist, Guard is
Linux only. docs/development.md has the steps, docs/install.md the apt
source.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -58,6 +58,7 @@ watch:
 * [configuration.md](docs/configuration.md): `/etc/guard/guard.yaml`
 * [presets.md](docs/presets.md): the presets, and writing your own patterns
 * [cli.md](docs/cli.md): the `guard` command
+* [development.md](docs/development.md): building, testing, releasing
 * [CHANGELOG.md](CHANGELOG.md)
 
 Housecarl's side: its [docs/bans.md](https://gitea.adbraun.lol/adam/housecarl/src/branch/main/docs/bans.md).