Fix 19 ESLint unused-variable errors across source and test files

Remove unused imports, functions, and variables flagged by
@typescript-eslint/no-unused-vars and no-useless-assignment rules.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/integration/forward-auth.test.ts

@@ -6,7 +6,6 @@ import {
   forwardAuthExchanges,
   forwardAuthAccess,
   groups,
-  groupMembers,
   users,
   proxyHosts
 } from '@/src/lib/db/schema';
@@ -26,10 +25,6 @@ function futureIso(seconds: number) {
   return new Date(Date.now() + seconds * 1000).toISOString();
 }
 
-function pastIso(seconds: number) {
-  return new Date(Date.now() - seconds * 1000).toISOString();
-}
-
 function hashToken(raw: string): string {
   return createHash('sha256').update(raw).digest('hex');
 }