Add Gitea self-hosted git server

Docker Compose stack (Gitea + Postgres) on port 3000, SSH on 2222,
reverse-proxied via Caddy at git.monotrope.au.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/Caddyfile

@@ -30,6 +30,13 @@ reader.monotrope.au {
 	encode zstd gzip
 }
 
+# Gitea
+git.monotrope.au {
+	reverse_proxy localhost:3000
+
+	encode zstd gzip
+}
+
 # GoatCounter analytics
 stats.monotrope.au {
 	reverse_proxy localhost:8081