fix: correct cancel_reason column name to cancellation_reason

Also add migration to drop remaining auth.users FK constraints
on p2p_messages, notifications, ratings, audit_log tables.

shared/lib/p2p-fiat.ts

@@ -888,7 +888,7 @@ export async function cancelTrade(
       .update({
         status: 'cancelled',
         cancelled_by: cancelledBy,
-        cancel_reason: reason,
+        cancellation_reason: reason,
       })
       .eq('id', tradeId);