fix: bundled dust cleanup — set-euo-pipefail (#516)

Add missing `set -euo pipefail` to three scripts per AGENTS.md conventions:
- lib/ci-helpers.sh
- lib/parse-deps.sh
- supervisor/supervisor-poll.sh

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

lib/ci-helpers.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+set -euo pipefail
 # ci-helpers.sh — Shared CI helper functions
 #
 # Source from any script: source "$(dirname "$0")/../lib/ci-helpers.sh"

lib/parse-deps.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+set -euo pipefail
 # parse-deps.sh — Extract dependency issue numbers from an issue body
 #
 # Usage: