feat(discount): admin Discount Management tab + uuid-based rule targets

Switch rule target references from int ids to uuids (frontend-friendly; the
engine compares uuids directly) via a migration. Add a Discount Management
tab to the subscription page with a full CRUD UI (DiscountTab): table + modal
form with per-type dynamic target fields (tenant tag / service cascade /
amount / visit count / specific patient / occasion + validity window),
priority and combinable/active toggles. Verified TSC + build.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

migrations/Version20260717082805.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20260717082805 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Switch discount_rules target reference columns from int id to uuid';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE discount_rules ADD target_tag_uuid VARCHAR(36) DEFAULT NULL, ADD target_record_uuid VARCHAR(36) DEFAULT NULL, ADD target_service_item_uuid VARCHAR(36) DEFAULT NULL, DROP target_tag_id, DROP target_record_id, DROP target_service_item_id');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE discount_rules ADD target_tag_id INT DEFAULT NULL, ADD target_record_id INT DEFAULT NULL, ADD target_service_item_id INT DEFAULT NULL, DROP target_tag_uuid, DROP target_record_uuid, DROP target_service_item_uuid');
+    }
+}