Reapply "feat(loyalty): EnakPoint & EnakCoin" (#32)

This reverts commit 4e24f9bbb0.

migrations/000096_create_customer_devices.up.sql

@@ -0,0 +1,17 @@
+-- Devices of the customer app, so customers can get push notifications through FCM
+-- (docs/prd-point-coin.md F5: the recipient of a transfer is notified). user_devices
+-- only holds staff devices.
+CREATE TABLE customer_devices (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    customer_id UUID NOT NULL REFERENCES customers(id) ON DELETE CASCADE,
+    device_id VARCHAR(255) NOT NULL,
+    platform VARCHAR(50) CHECK (platform IN ('android', 'ios', 'web')),
+    fcm_token VARCHAR(512) NOT NULL,
+    app_version VARCHAR(50),
+    last_active_at TIMESTAMP WITH TIME ZONE,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);
+
+CREATE UNIQUE INDEX idx_customer_devices_customer_device ON customer_devices(customer_id, device_id);
+CREATE INDEX idx_customer_devices_fcm_token ON customer_devices(fcm_token);