Set the default language of demo users to Catalan

Since i have my browser in English, the automatically detected language
is also set in English, making it harder for me to see if i added all
the translations; when the language is Catalan, i can see the
untranslated strings.

demo/demo.sql

@@ -4,9 +4,9 @@ begin;
 set search_path to camper, auth, public;
 
 alter table auth."user" alter column user_id restart with 42;
-insert into auth."user" (email, name, password)
-values ('demo@camper', 'Demo User', 'demo')
-     , ('admin@camper', 'Demo Admin', 'admin')
+insert into auth."user" (email, name, password, lang_tag)
+values ('demo@camper', 'Demo User', 'demo', 'ca')
+     , ('admin@camper', 'Demo Admin', 'admin', 'ca')
 ;
 
 alter table company alter column company_id restart with 52;