feat: improve agent workbench and digital human flows

migrations/20260624000001_restore_new_user_starter_credit.sql

@@ -0,0 +1,13 @@
+-- Restore the documented $1 starter credit for existing user default keys.
+-- Keep explicit admin/recharge limits intact, and never leave default user keys
+-- with NULL max_cost because NULL is treated as unlimited by the proxy path.
+UPDATE downstream_api_keys
+SET max_cost = 1.0,
+    updated_at = datetime('now')
+WHERE user_id IS NOT NULL
+  AND (max_cost IS NULL OR max_cost <= 0.0)
+  AND (
+      name LIKE '% 的默认密钥'
+      OR name LIKE '% default key'
+      OR key LIKE 'sk-user-%'
+  );