Merge parent_id migration into single 2026021000 upgrade script

SQL/postgres/2026021000.sql

@@ -51,3 +51,9 @@ ALTER TABLE ident_switch
 	ADD notify_desktop
 		smallint
 		DEFAULT NULL;
+
+-- Add alias support: parent_id links an alias identity to a parent account
+ALTER TABLE ident_switch
+	ADD parent_id integer DEFAULT NULL;
+
+CREATE INDEX IX_ident_switch_parent_id ON ident_switch(parent_id);