schema: Require role.email always be lowercase

Otherwise it will silently fail to match in the application.

postgres/schema.sql

@@ -131,7 +131,8 @@ CREATE TABLE nodes (
 );
 
 CREATE TABLE roles (
-	email TEXT PRIMARY KEY,
+	-- email should always be lowercase since that's how the auth function compares it
+	email TEXT PRIMARY KEY CHECK email = lower(email),
 	name TEXT NOT NULL,
 	editor BOOLEAN NOT NULL DEFAULT FALSE,
 	artist BOOLEAN NOT NULL DEFAULT FALSE