fix(ads): ref_slug no longer truncates past campaign 999

lpad(seq::text, 3, '0') truncates longer strings, so campaign 1000 became
crawlproof-ad-100 and every new campaign hit ad_campaigns_ref_slug_key.
Pad to at least three digits; existing slugs are unchanged. Applied to prod.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: ralyodio

supabase/migrations/20261014120000_ad_ref_slug_past_999.sql

@@ -0,0 +1,7 @@
+-- ref_slug was 'crawlproof-ad-' || lpad(seq::text, 3, '0'). lpad TRUNCATES a
+-- longer string to the target length, so campaign 1000 became crawlproof-ad-100
+-- and every insert after the 999th hit ad_campaigns_ref_slug_key. Pad to at
+-- least three digits instead: 001..999 are unchanged, 1000+ keep every digit.
+alter table public.ad_campaigns
+  alter column ref_slug set expression as
+    ('crawlproof-ad-' || lpad(seq::text, greatest(3, length(seq::text)), '0'));