Expand ROUTE_GUARD_TIERS.md Tier 1 (LOCAL_ONLY):
- link the GHSA advisory and explain the attack class (RCE via a subprocess spawn
reachable from non-loopback traffic)
- replace the 3-example prefix table with the full LOCAL_ONLY set, mirroring
LOCAL_ONLY_API_PREFIXES / LOCAL_ONLY_API_PATTERNS in routeGuard.ts (the
authoritative source; check-route-guard-membership enforces the code side)
- add an "Operator guidance & auditing" section for users behind
nginx/Cloudflare/Tailscale: don't forge X-Forwarded-For loopback, keep the
manage-scope bypass minimal, and how to audit non-loopback access
Docs-only; SECURITY.md already links here.
Closes#5599
aa0ac7da87