fix: Docker stack: edge proxy + staging container from bootstrap (#1)

- Add edge (Caddy) service to docker-compose.yml as reverse proxy for
  Forgejo (/forgejo/*), Woodpecker (/ci/*), and staging (default)
- Replace placeholder staging service with Caddy-based static file server
- Generate docker/Caddyfile template during disinto init
- Generate default "Nothing shipped yet" staging page in docker/staging-seed/
- Add caddy_data and staging-site volumes
- Staging container seeds default page on first boot; CI overwrites later

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/smoke-init.sh

@@ -26,7 +26,9 @@ pass() { printf 'PASS: %s\n' "$*"; }
 cleanup() {
   rm -rf "$MOCK_BIN" "$MOCK_STATE" /tmp/smoke-test-repo \
          "${FACTORY_ROOT}/projects/smoke-repo.toml" \
-         "${FACTORY_ROOT}/docker-compose.yml"
+         "${FACTORY_ROOT}/docker-compose.yml" \
+         "${FACTORY_ROOT}/docker/Caddyfile" \
+         "${FACTORY_ROOT}/docker/staging-seed"
   # Restore .env only if we created the backup
   if [ -f "${FACTORY_ROOT}/.env.smoke-backup" ]; then
     mv "${FACTORY_ROOT}/.env.smoke-backup" "${FACTORY_ROOT}/.env"