fix: guard against undefined fields when loading old localStorage data

Old entries in localStorage lack new fields (department, role, contactPersons,
linkedEntryIds, attachments, versions, placeholders, ipAddress, vendor, model).
Add null-coalescing guards to prevent client-side crashes on property access.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/modules/it-inventory/hooks/use-inventory.ts

@@ -79,9 +79,9 @@ export function useInventory() {
         item.name.toLowerCase().includes(q) ||
         item.serialNumber.toLowerCase().includes(q) ||
         item.assignedTo.toLowerCase().includes(q) ||
-        item.ipAddress.toLowerCase().includes(q) ||
-        item.vendor.toLowerCase().includes(q) ||
-        item.model.toLowerCase().includes(q)
+        (item.ipAddress ?? '').toLowerCase().includes(q) ||
+        (item.vendor ?? '').toLowerCase().includes(q) ||
+        (item.model ?? '').toLowerCase().includes(q)
       );
     }
     return true;