chore(lint): remove all 34 dead-code warnings (verified site by site)

unused-vars (25): leftover imports/types across pages, routes and services;
write-only sickHours accumulator; unused holidayCount pair; test helpers
authPatch/authDelete; TOut dropped from ApiMutationOptions (the hook keeps
its own generic — no call-site changes); requireAuth no longer importable
in customers/warehouse routes (matches the no-bare-auth-reads convention).

useless-assignment (5): initializers proven overwritten on every path
(systemQty x2, hours, writtenSize -> let x: number) and the seed's dead
adminUser reassignment (create kept, assignment dropped).

useless-escape (4): [eE+\-] -> [eE+-] and [\/...] -> [/...] — identical
semantics.

Behavior-neutral; lint 102 -> 68 warnings (0 errors), suite 641 green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/components/PlanCellModal.tsx

@@ -148,7 +148,7 @@ const TrashIcon = (
 );
 
 export default function PlanCellModal(props: Props) {
-  const { open, mode, onClose } = props;
+  const { open, mode } = props;
   if (!open || mode.kind === "closed") return null;
   if (mode.kind === "view") return <ViewModal {...props} />;
   if (mode.kind === "day-in-range")