Updater-Migration für Feature-Tabellen + README um neue Features erweitern

- updater/migrations/0001_feature_ui_tables.sql: legt voucher_templates und
  password_reset_tokens idempotent an (CREATE TABLE IF NOT EXISTS), damit
  bestehende Installationen die neuen Tabellen per System-Update erhalten
- Updater-UI: Button "Ausstehende Migrationen ausführen" + run_migrations-Action
  (CSRF-geschützt) im Migrations-Tab
- README: Features (Bulk, Templates, Dark Mode, i18n, Audit-Log, Passwort-Reset),
  zwei neue Screenshots (Bulk-Erstellung, Dashboard Dark Mode), Roadmap & Updater-
  Abschnitt aktualisiert

updater/migrations/0001_feature_ui_tables.sql

@@ -0,0 +1,29 @@
+-- Updater-Migration: Tabellen der UI/Feature-Erweiterung fuer bestehende
+-- Installationen nachziehen (Voucher-Templates + Password-Reset-Tokens).
+-- Idempotent (CREATE TABLE IF NOT EXISTS) – auf frischen Installationen, die
+-- database.sql bereits enthalten, ein No-Op.
+
+CREATE TABLE IF NOT EXISTS `voucher_templates` (
+  `id` INT PRIMARY KEY AUTO_INCREMENT,
+  `name` VARCHAR(255) NOT NULL,
+  `max_uses` INT NOT NULL DEFAULT 1,
+  `expire_minutes` INT NOT NULL DEFAULT 480,
+  `description` VARCHAR(500),
+  `is_active` TINYINT(1) DEFAULT 1,
+  `created_by` INT,
+  `created_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  `updated_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  FOREIGN KEY (`created_by`) REFERENCES `users`(`id`) ON DELETE SET NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+CREATE TABLE IF NOT EXISTS `password_reset_tokens` (
+  `id` INT PRIMARY KEY AUTO_INCREMENT,
+  `user_id` INT NOT NULL,
+  `token` VARCHAR(128) NOT NULL,
+  `expires_at` TIMESTAMP NOT NULL,
+  `used` TINYINT(1) DEFAULT 0,
+  `created_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  FOREIGN KEY (`user_id`) REFERENCES `users`(`id`) ON DELETE CASCADE,
+  UNIQUE KEY `unique_token` (`token`),
+  INDEX `idx_expires` (`expires_at`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;