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/address-book/hooks/use-contacts.ts

@@ -76,8 +76,8 @@ export function useContacts() {
         c.company.toLowerCase().includes(q) ||
         c.email.toLowerCase().includes(q) ||
         c.phone.includes(q) ||
-        c.department.toLowerCase().includes(q) ||
-        c.role.toLowerCase().includes(q)
+        (c.department ?? '').toLowerCase().includes(q) ||
+        (c.role ?? '').toLowerCase().includes(q)
       );
     }
     return true;