bug(computer-server/agent): Fix scroll and drag on Anthropic models

[ddupont808]

Currently the scroll tool and the drag tool fail on Anthropic models, which can be verified by running the following evals:

• cb run fill-form --dataset cua-bench-basic --agent cua-agent --model claude-opus-4.5 (Requires scroll for 100% pass)
• cb run drag-drop --dataset cua-bench-basic --agent cua-agent --model claude-opus-4.5 (Requires drag for 100% pass)

Problem:

• The model is unable to scroll in the desired direction / magnitude
• The model drag end position has incorrect coordinates

Possible causes:

• Incorrect parsing of the 2nd coordinate
• Current mapping of the scroll direction / magnitude is not what is expected by the anthropic computer tool