claude-in-chrome: always opens new window for MCP tab group instead of reusing existing window

When the extension initializes its MCP tab group (getOrCreateMcpTabContext), it always calls chrome.windows.create(), opening a new browser window even when an existing normal window is already open.

Steps to reproduce

1. Have Edge or Chrome open with one or more existing windows
2. Connect Claude Code via the claude-in-chrome extension
3. A second "Personal" window opens containing the MCP tab group

Expected behavior

MCP tab group is created as a new tab in the existing focused window, not a new window.

Actual behavior

chrome.windows.create() is always called, producing a duplicate browser window.

Suggested fix

In getOrCreateMcpTabContext, call chrome.windows.getLastFocused({windowTypes: ["normal"]}) first and create the tab in that window. Only fall back to chrome.windows.create() if no existing window is available.

Environment

• Extension version: 1.0.75
• Browser: Microsoft Edge (also reproducible in Chrome)
• OS: Windows 11