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';

prisma/schema.prisma

@@ -76,6 +76,19 @@ model audit_logs {
   @@fulltext([description], map: "idx_audit_search")
 }
 
+model ai_usage {
+  id            Int      @id @default(autoincrement())
+  user_id       Int?
+  kind          String   @db.VarChar(20)
+  model         String   @db.VarChar(50)
+  input_tokens  Int      @default(0)
+  output_tokens Int      @default(0)
+  cost_usd      Decimal  @default(0) @db.Decimal(10, 6)
+  created_at    DateTime @default(now()) @db.Timestamp(0)
+
+  @@index([created_at], map: "idx_ai_usage_created")
+}
+
 model bank_accounts {
   id             Int       @id @default(autoincrement())
   account_name   String?   @db.VarChar(255)
@@ -134,6 +147,7 @@ model company_settings {
   warehouse_issue_number_pattern    String?   @db.VarChar(100)
   warehouse_inventory_prefix        String?   @db.VarChar(20)
   warehouse_inventory_number_pattern String?   @db.VarChar(100)
+  ai_monthly_budget_usd Decimal? @default(50.00) @db.Decimal(10, 2)
 }
 
 model customers {