Add lab restream pipeline with pirate_drift logo and lib/env.sh.

Encode-once/fanout scripts, HLS output, and single overloadable env source.
Commits assets/pirate_drift.png as default watermark for cluster runs.

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

bin/stop.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+# shellcheck disable=SC1091
+source "${ROOT}/lib/common.sh"
+
+stop_pidfile() {
+  local pf="$1"
+  [[ -f "${pf}" ]] || return 0
+  local pid
+  pid="$(cat "${pf}")"
+  if kill -0 "${pid}" 2>/dev/null; then
+    kill "${pid}" 2>/dev/null || true
+    sleep 1
+    kill -9 "${pid}" 2>/dev/null || true
+  fi
+  rm -f "${pf}"
+}
+
+stop_pidfile "${RUN_DIR}/fanout.pid"
+stop_pidfile "${RUN_DIR}/encode.pid"
+pkill -f "${ROOT}/bin/fanout-copy.sh" 2>/dev/null || true
+pkill -f "${ROOT}/bin/encode-once.sh" 2>/dev/null || true
+remove_pipe
+rm -f "${ROOT}/.intro_shown" "${ROOT}/.current_source" 2>/dev/null || true
+log "pipeline stopped"