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>

scripts/migrate-received-invoices-to-nas.ts

@@ -59,7 +59,7 @@ async function main() {
     // fails we KEEP file_data and report the row as failed.
     const expectedSize = rec.file_data.length;
     const readBack = nasFinancialsManager.readReceivedInvoice(result.filePath);
-    let writtenSize = -1;
+    let writtenSize: number;
     if (readBack) {
       writtenSize = readBack.data.length;
     } else {