[FEATURE] Implement Screenshot Region Selection

[saketsarin]

Describe the solution you'd like
Add an option to select and capture only a specific region of the page, rather than always capturing the entire page.

Tasks

• Add new command to capture a selected region
• Implement UI overlay in browser for region selection
• Update screenshot capture logic to respect selected region
• Add button in status bar for region selection

Technical Details

• Extend Chrome DevTools Protocol interaction in src/browser/commands
• Implement region selection UI using browser injection
• Chrome DevTools Protocol supports capturing specific regions via the Page.captureScreenshot method with clip parameters

Potential Implementation
Inject a UI overlay into the page that allows the user to drag and select a region, then capture that region using the CDP Page.captureScreenshot method with the appropriate clip rectangle parameters.