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>

prisma/seed.ts

@@ -391,12 +391,12 @@ async function main() {
   console.log(`  Admin role now has all ${allPerms.length} permissions`);
 
   // 4. Ensure admin user exists
-  let adminUser = await prisma.users.findFirst({
+  const adminUser = await prisma.users.findFirst({
     where: { username: "admin" },
   });
   if (!adminUser) {
     const hash = bcrypt.hashSync("admin", 10);
-    adminUser = await prisma.users.create({
+    await prisma.users.create({
       data: {
         username: "admin",
         email: "admin@boha.local",