feat: alert captains when decisions need attention

[alimohammad-123]

What Changed

• Add bounded, privacy-safe, deduplicated alerts for open captain decisions, durable decision holds, and explicit prompts, with macOS, Herdr, and custom command channels.
• Integrate decision scanning into watcher and heartbeat flows, and centralize safe notification execution for decision and wedge alerts.
• Harden secondmate home rollback and charter validation, transient Treehouse worktree discovery, and Herdr prompt matching.

Risk Assessment

✅ Low: Captain, the change is well-bounded and no material source risks were substantiated in the full review pass.

Testing

Completed 1 recorded test check.

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

✅ **Review** - passed

✅ No issues found.

✅ **Test** - passed

✅ No issues found.

• command -v tmux >/dev/null || { echo "tmux is required for e2e tests" >&2; exit 1; }; tmux -V; rc=0; for t in tests/*.test.sh; do echo "== $t =="; bash "$t" || rc=1; done; exit "$rc"

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.