bug(computer-server): scroll command requires x,y on Android but API doesn't document this

[f-trycua]

Description

The scroll command on Android requires x and y parameters, but calling it with just direction fails with a confusing error.

Steps to Reproduce

curl -X POST http://localhost:8000/cmd -H "Content-Type: application/json" \
  -d '{"command":"scroll","params":{"direction":"down"}}'

Error

{"success": false, "error": "AndroidAutomationHandler.scroll() missing 2 required positional arguments: 'x' and 'y'"}

Expected Behavior

Either:

1. The scroll command should work with just direction (using screen center as default)
2. Or the error message should clearly indicate that x and y are required on Android

Suggested Fix

In AndroidAutomationHandler.scroll(), provide default values for x and y:

async def scroll(self, direction: str, x: int = None, y: int = None, amount: int = 1):
    if x is None or y is None:
        # Use screen center as default
        screen_size = await self.get_screen_size()
        x = x or screen_size['width'] // 2
        y = y or screen_size['height'] // 2
    # ... rest of implementation

Environment

• cua-computer-server: 0.3.9
• Platform: Android 11 (emulator)