Implement database schema for scheduled XAP launch (#3095)

This commit implements the database schema changes for the Expiry Access Period (XAP) launch configuration on TLDs. It represents the first step of a Two-PR deployment strategy, deploying the database schema changes in advance of the server logic.

Specifically, it replaces the `expiry_access_period_enabled` boolean column (originally introduced in PR #2804) with a new `expiry_access_period_transitions` hstore column.

Why we are making this change:
A basic boolean flag only allows an immediate, manual on/off toggle. To launch XAP on a TLD, registry operators would have to manually flip the flag at the exact launch time, which is operationally fragile and cannot be planned in advance. Refactoring this to an hstore-backed timed transition map (mapping Instant to ExpiryAccessPeriodMode) allows operators to schedule the XAP launch in advance via TLD YAML configurations. The registry will automatically transition the TLD to the ENABLED mode at the scheduled timestamp, aligning with how other scheduled TLD changes (like TLD states and EAP fee schedules) are managed.

Since the original boolean column was never mapped in Java (PR #2804 only added the database column), it is completely safe to drop it immediately in this migration.

To ensure backward compatibility with running servers (which are still executing the old Java code during the deployment transition), the new column is added as `NOT NULL` with a temporary `DEFAULT` constraint. This prevents constraint violations on inserts from old servers. A TODO has been left in the SQL migration to drop this default in a subsequent schema release once the Java changes have been deployed.

TAG=agy
CONV=88271e71-e272-40e0-85f8-a075a423b7c2

db/src/main/resources/sql/flyway.txt

@@ -220,3 +220,4 @@ V219__domain_history_package_token_idx.sql
 V220__domain_package_token_idx.sql
 V221__remove_contact_history.sql
 V222__remove_contact.sql
+V223__tld_change_xap_enabled_to_transitions.sql

db/src/main/resources/sql/flyway/V223__tld_change_xap_enabled_to_transitions.sql

@@ -0,0 +1,25 @@
+-- Copyright 2026 The Nomulus Authors. All Rights Reserved.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+-- Drop the old unused boolean column. Since it was never mapped in Tld.java
+-- on master, no running servers map or use it, making it completely safe to drop.
+ALTER TABLE "Tld" DROP COLUMN expiry_access_period_enabled;
+
+-- Add the new transitions column as NOT NULL with a temporary DEFAULT value to
+-- ensure backward compatibility with the running servers (old Java code) during
+-- the transition phase of the deployment.
+-- TODO(mcilwain): Drop this DEFAULT constraint in a subsequent schema release
+-- once the Java code mapping this column has been fully deployed.
+ALTER TABLE "Tld" ADD COLUMN expiry_access_period_transitions hstore
+    DEFAULT '"1970-01-01T00:00:00.000Z"=>"DISABLED"'::hstore NOT NULL;

db/src/main/resources/sql/schema/nomulus.golden.sql

@@ -1205,7 +1205,7 @@ CREATE TABLE public."Tld" (
     breakglass_mode boolean DEFAULT false NOT NULL,
     bsa_enroll_start_time timestamp with time zone,
     create_billing_cost_transitions public.hstore NOT NULL,
-    expiry_access_period_enabled boolean DEFAULT false NOT NULL
+    expiry_access_period_transitions public.hstore DEFAULT '"1970-01-01T00:00:00.000Z"=>"DISABLED"'::public.hstore NOT NULL
 );