Feat: request user input tool (#9472)

### Summary
* Add `requestUserInput` tool that the model can use for gather
feedback/asking question mid turn.


### Tool input schema
```
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "requestUserInput input",
  "type": "object",
  "additionalProperties": false,
  "required": ["questions"],
  "properties": {
    "questions": {
      "type": "array",
      "description": "Questions to show the user (1-3). Prefer 1 unless multiple independent decisions block progress.",
      "minItems": 1,
      "maxItems": 3,
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": ["id", "header", "question"],
        "properties": {
          "id": {
            "type": "string",
            "description": "Stable identifier for mapping answers (snake_case)."
          },
          "header": {
            "type": "string",
            "description": "Short header label shown in the UI (12 or fewer chars)."
          },
          "question": {
            "type": "string",
            "description": "Single-sentence prompt shown to the user."
          },
          "options": {
            "type": "array",
            "description": "Optional 2-3 mutually exclusive choices. Put the recommended option first and suffix its label with \"(Recommended)\". Only include \"Other\" option if we want to include a free form option. If the question is free form in nature, do not include any option.",
            "minItems": 2,
            "maxItems": 3,
            "items": {
              "type": "object",
              "additionalProperties": false,
              "required": ["value", "label", "description"],
              "properties": {
                "value": {
                  "type": "string",
                  "description": "Machine-readable value (snake_case)."
                },
                "label": {
                  "type": "string",
                  "description": "User-facing label (1-5 words)."
                },
                "description": {
                  "type": "string",
                  "description": "One short sentence explaining impact/tradeoff if selected."
                }
              }
            }
          }
        }
      }
    }
  }
}
```

### Tool output schema
```
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "requestUserInput output",
  "type": "object",
  "additionalProperties": false,
  "required": ["answers"],
  "properties": {
    "answers": {
      "type": "object",
      "description": "Map of question id to user answer.",
      "additionalProperties": {
        "type": "object",
        "additionalProperties": false,
        "required": ["selected"],
        "properties": {
          "selected": {
            "type": "array",
            "items": { "type": "string" }
          },
          "other": {
            "type": ["string", "null"]
          }
        }
      }
    }
  }
}
```

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -606,7 +606,8 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             | EventMsg::SkillsUpdateAvailable
             | EventMsg::UndoCompleted(_)
             | EventMsg::UndoStarted(_)
-            | EventMsg::ThreadRolledBack(_) => {}
+            | EventMsg::ThreadRolledBack(_)
+            | EventMsg::RequestUserInput(_) => {}
         }
         CodexStatus::Running
     }