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)

assets/oh-my-opencode.schema.json

@@ -960,6 +960,9 @@
                 }
               },
               "additionalProperties": false
+            },
+            "allow_non_gpt_model": {
+              "type": "boolean"
             }
           },
           "additionalProperties": false
@@ -3248,6 +3251,11 @@
           "prompt_append": {
             "type": "string"
           },
+          "max_prompt_tokens": {
+            "type": "integer",
+            "exclusiveMinimum": 0,
+            "maximum": 9007199254740991
+          },
           "is_unstable_agent": {
             "type": "boolean"
           },