feat(ai): add @anthropic-ai/sdk, ai_usage table, ai.use permission

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/migrations/20260608120000_add_ai_assistant/migration.sql

@@ -0,0 +1,29 @@
+-- AI assistant (Phase 1): usage-tracking table, monthly budget column, ai.use permission.
+
+CREATE TABLE `ai_usage` (
+  `id` INTEGER NOT NULL AUTO_INCREMENT,
+  `user_id` INTEGER NULL,
+  `kind` VARCHAR(20) NOT NULL,
+  `model` VARCHAR(50) NOT NULL,
+  `input_tokens` INTEGER NOT NULL DEFAULT 0,
+  `output_tokens` INTEGER NOT NULL DEFAULT 0,
+  `cost_usd` DECIMAL(10, 6) NOT NULL DEFAULT 0,
+  `created_at` TIMESTAMP(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0),
+  PRIMARY KEY (`id`),
+  INDEX `idx_ai_usage_created` (`created_at`)
+) DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+
+ALTER TABLE `company_settings`
+  ADD COLUMN `ai_monthly_budget_usd` DECIMAL(10, 2) NULL DEFAULT 50.00;
+
+-- ai.use permission + grant to admin (INSERT IGNORE → idempotent), mirroring
+-- the warehouse-permissions migration.
+INSERT IGNORE INTO `permissions` (`name`, `display_name`, `module`, `description`, `created_at`) VALUES
+  ('ai.use', 'AI asistent', 'ai', 'Používat AI asistenta (chat a import faktur)', NOW());
+
+INSERT IGNORE INTO `role_permissions` (`role_id`, `permission_id`)
+SELECT r.id, p.id
+FROM   `roles` r
+CROSS  JOIN `permissions` p
+WHERE  r.name = 'admin'
+  AND  p.name = 'ai.use';