feat(pages): add select_foreground_page tool to detect and select the visible browser tab

[santhreal]

Summary

Adds a new select_foreground_page tool that detects and selects the browser tab currently visible to the user.

Fixes #933

Problem

When connecting to an existing browser with --autoConnect, the MCP-selected page often doesn't match the tab the user is actually looking at. The [selected] tag in list_pages reflects MCP's internal selection (defaults to pages[0]), not the browser's foreground tab. Users have to:

1. list_pages
2. Manually identify which page they're looking at
3. select_page with the correct ID

Solution

The new select_foreground_page tool queries document.visibilityState on every open page via page.evaluate(). If exactly one page reports "visible", it is automatically selected.

Why document.visibilityState?

• It's a standard web API available on all pages
• Puppeteer's bringToFront() correctly updates it
• When a user switches tabs in Chrome, the foreground tab reports "visible" and background tabs report "hidden"
• No experimental CDP APIs needed

Graceful fallback

If visibility can't be determined (e.g. all pages hidden, multiple visible, or evaluate() fails on chrome:// pages), the tool reports failure and suggests using select_page manually.

Changes

File	Change
src/McpContext.ts	Add selectForegroundPage() method
src/tools/pages.ts	Add select_foreground_page tool definition
src/tools/ToolDefinition.ts	Add selectForegroundPage to Context type
src/bin/chrome-devtools-cli-options.ts	Add CLI entry
tests/tools/pages.test.ts	Add tests for foreground detection and fallback

Example workflow

User: "take a snapshot of the page I'm looking at"
Agent calls: select_foreground_page
→ Selected page 3 (https://docs.example.com) as the foreground tab.
Agent calls: take_snapshot
→ Returns snapshot of the correct page

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