Add IP_HEADER env var to override client IP source

Allows customers behind an upstream proxy (eg. zScaler, Imperva) to point
the worker at a different header (typically x-forwarded-for) so the real
client IP, rather than the proxy egress IP, is sent to the CrowdHandler
API. For multi-value headers the left-most entry is used. Falls back to
cf-connecting-ip if the configured header is missing/empty or anything
throws, so existing deployments are unaffected.

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

Author: luke-owen-crowdhandler

dist/README.md

@@ -1 +1 @@
-This folder contains the built output assets for the worker "crowdhandler-integration" generated at 2026-04-27T14:01:55.277Z.
+This folder contains the built output assets for the worker "crowdhandler-integration" generated at 2026-06-09T11:27:13.384Z.