docs: log Node 20 actions deprecation in backlog

CI annotations on the v0.1 baseline runs flag actions/checkout,
actions/setup-python, and gitleaks/gitleaks-action as running on
Node 20, deprecated as of 2026-09-16 with a forced upgrade on
2026-06-02. Captured as B003 so it doesn't drift past the deadline.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: RyanAlberts

BACKLOG.md

@@ -16,6 +16,7 @@ Promoted to GitHub issues when an item survives more than one PR. ADRs for non-t
 
 - [B001] yc-oss/api is now sole source for batch listing — the previously planned `ycombinator.com/companies?batch=...` fallback is disallowed by robots.txt. PR #1 must implement a hard-fail path when yc-oss is unreachable, plus an upstream-staleness CI cron. — surfaced in: phase 0 verification — proposed: PR #1
 - [B002] Confirm Cloudflare or upstream caching on `yc-oss.github.io/api/*` for our use case (rate limit headroom on full-batch sweeps). — surfaced in: phase 0 — proposed: PR #1
+- [B003] CI annotations report Node 20 actions deprecated (forced to Node 24 from 2026-06-02). Refresh `actions/checkout`, `actions/setup-python`, `gitleaks/gitleaks-action` to Node-24-compatible majors before that date. — surfaced in: phase 0 CI run — proposed: ad-hoc PR before 2026-06-02
 
 ## Done