Customers can view and cancel their booking through a link in the e-mail. Fixes #18

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

migrations/10_customer_cancel.sql

@@ -0,0 +1,4 @@
+-- Customers can cancel their bookings through a link in the e-mail
+-- How many hours before the start of a booking the customer may still cancel it, 0 = until the start
+ALTER TABLE company ADD cancel_hours INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE reservation_sum ADD canceled_by_customer BOOLEAN NOT NULL DEFAULT false;

migrations/11_customer_canceled_message.sql

@@ -0,0 +1,4 @@
+-- no-transaction
+-- E-mail for the staff about a booking cancelled by the customer. A new enum value can't be
+-- added inside a transaction on older PostgreSQL versions, hence the separate file.
+ALTER TYPE message_type ADD VALUE IF NOT EXISTS 'CustomerCanceled';