fix(database): enable pg_net extension

Install the extension required by notification triggers and cron jobs so fresh local and preview databases expose net.http_post before fixtures are seeded.

apps/supabase/migrations/20260827212552_enable_pg_net_extension.sql

@@ -0,0 +1,4 @@
+-- Notification triggers and scheduled jobs call net.http_post.
+-- Keep the extension in migrations so clean local and preview databases have
+-- the same dependency as hosted environments.
+CREATE EXTENSION IF NOT EXISTS pg_net WITH SCHEMA extensions;