feat(runner): add Gitea act_runner docker setup

Compose service registers against git.wampler.us via act_runner,
mounts docker.sock for job execution. Secrets and runtime state
(.env, data/) kept out of git.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -2,3 +2,4 @@
 *.kate-swp
 .env
 **/.env
+runner/data/