feat: add default_hours_scheduled_changes table and admin_notifications enum value

Add new table for staging future default hours changes with an upsert guard (at most one pending change). Extend admin_notification_reason enum with 'default_hours_changed'.

init-scripts/init-script.sql

@@ -552,6 +552,23 @@ INSERT INTO working_hours VALUES (4, '09:00:00', '17:00:00', TRUE);
 INSERT INTO working_hours VALUES (5, '09:00:00', '17:00:00', TRUE);
 INSERT INTO working_hours VALUES (6, '00:00:00', '00:00:00', FALSE);
 
+-- =======================================
+-- SCHEDULED DEFAULT HOURS CHANGES
+-- =======================================
+CREATE TABLE default_hours_scheduled_changes (
+    id SERIAL PRIMARY KEY,
+    effective_date DATE NOT NULL,
+    created_by CHAR(12) REFERENCES users(id),
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    applied_at TIMESTAMPTZ,
+    cancelled_at TIMESTAMPTZ,
+    hours JSONB NOT NULL
+);
+
+CREATE UNIQUE INDEX idx_one_pending_change
+    ON default_hours_scheduled_changes ((1))
+    WHERE applied_at IS NULL AND cancelled_at IS NULL;
+
 -- =======================================
 -- EXCEPTIONAL WORKING HOURS
 -- =======================================
@@ -800,7 +817,7 @@ INSERT INTO business_settings (
     'https://www.website.co.uk'
 );
 
-CREATE TYPE admin_notification_reason AS ENUM ('pending_booking', 'cancelled_booking', 'rescheduled_booking', '1_week_no_pay', '1_month_no_pay', 'affiliate_claim', 'late_cancellation', 'deposit_paid', 'edit_request', 'edit_requested', 'new_booking', 'deposit_not_paid_by_deadline', 'gift_card_purchased_for_friend');
+CREATE TYPE admin_notification_reason AS ENUM ('pending_booking', 'cancelled_booking', 'rescheduled_booking', '1_week_no_pay', '1_month_no_pay', 'affiliate_claim', 'late_cancellation', 'deposit_paid', 'edit_request', 'edit_requested', 'new_booking', 'deposit_not_paid_by_deadline', 'gift_card_purchased_for_friend', 'default_hours_changed');
 
 CREATE TABLE admin_notifications (
     id CHAR(12) PRIMARY KEY DEFAULT generate_admin_notifications_id(),