test(plugin-auth): type the forwarding-header fixtures as header records

The declared-trust pins passed an inferred union of two object literals
(each with the other key optional-undefined) where through() takes a
Record of strings: TS2345 twice under tsconfig.test.json.

Claude-Session: https://claude.ai/code/session_01UmqzD97e14iws6hmVhgZ5y
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/plugins/plugin-auth/src/bridge-redispatch-transport.pin.test.ts

@@ -287,9 +287,9 @@ async function through(
 }
 
 /** What a caller sends with no trusted proxy declared: forwarding headers naming another address. */
-const CLAIMED_FORWARDING = { 'x-forwarded-for': CLAIMED, 'x-real-ip': CLAIMED };
+const CLAIMED_FORWARDING: Record<string, string> = { 'x-forwarded-for': CLAIMED, 'x-real-ip': CLAIMED };
 /** What a declared trusted proxy forwards, in each of the two spellings the rule reads. */
-const PROXY_FORWARDING = [
+const PROXY_FORWARDING: Record<string, string>[] = [
   { 'x-forwarded-for': `${FORWARDED_CLIENT}, ${PROXY_HOP}` },
   { 'x-real-ip': FORWARDED_CLIENT },
 ];