Summary

This PR adds an optional display parameter to Snapshot so callers can limit the returned snapshot to specific monitors, such as display=[0] or display=[0,1].

Changes

• filter Snapshot screenshot output to the selected display region
• filter focused and opened windows to the selected display region
• filter interactive and scrollable elements to the selected display region
• add metadata describing the selected displays and screenshot region
• keep the default behavior unchanged when display is omitted

Why this approach

This is a small and low-risk change focused on Snapshot, where multi-monitor ambiguity is most visible to the LLM.

A more complete solution would be to add display support to all tools, but that would require broader coordinate translation changes, introduce more maintenance overhead, and increase complexity for a case that may affect a smaller portion of users.

Benefits

• improves LLM awareness in multi-monitor scenarios by returning a more coherent view
• improves screenshot clarity when only one display is needed, since Snapshot output is capped at 1080p and full dual-monitor captures can become blurry

Closes #77