refactor(ultrawork): remove thinking config injection from model override

Delegate thinking config control to the provider layer rather than
injecting it manually in ultrawork model override.

🤖 Generated with assistance of [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/plugin/ultrawork-db-model-override.ts

@@ -21,11 +21,10 @@ function tryUpdateMessageModel(
   )
   const result = stmt.run(targetModel.providerID, targetModel.modelID, messageId)
   if (result.changes === 0) return false
-
   if (variant) {
     db.prepare(
-      `UPDATE message SET data = json_set(data, '$.variant', ?, '$.thinking', ?) WHERE id = ?`,
-    ).run(variant, variant, messageId)
+      `UPDATE message SET data = json_set(data, '$.variant', ?) WHERE id = ?`,
+    ).run(variant, messageId)
   }
   return true
 }