feat: auto-refresh AJAX, bouton transfert entre comptes, webhook par compte

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

sql/schema.sql

@@ -27,6 +27,7 @@ CREATE TABLE IF NOT EXISTS accounts (
     email        VARCHAR(200) NOT NULL UNIQUE,
     display_name VARCHAR(100),
     smb_path     VARCHAR(255) NOT NULL,
+    webhook_url  VARCHAR(500) NULL,
     active       TINYINT(1) NOT NULL DEFAULT 1,
     created_at   DATETIME DEFAULT NOW()
 );