Initial Ladill Hosting app with Gitea deploy pipeline.

Shared web hosting extracted from the platform monolith, with CI deploy
to /var/www/ladill-hosting matching Bird/Domains/Email.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/bin/ladill-hosting-user

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  echo "Usage: ladill-hosting-user <username> <base64-command>" >&2
+  exit 64
+}
+
+[[ $# -eq 2 ]] || usage
+
+username="$1"
+payload_b64="$2"
+
+if [[ ! "$username" =~ ^[A-Za-z_][A-Za-z0-9_-]*$ ]]; then
+  echo "Invalid username: $username" >&2
+  exit 64
+fi
+
+command="$(printf '%s' "$payload_b64" | base64 --decode)"
+
+exec runuser -u "$username" -- bash -lc "$command"