VS Code: Add setting to open review diffs in active editor group instead of split

Problem

When Claude Code opens a review/diff view (e.g., plan approval, proposed file changes), it always opens in a new editor group (split layout), creating an unwanted split.

This is problematic because:

• On small screens or laptops, the split makes both panels too narrow to read comfortably
• Users who prefer a single editor group workflow are forced into splits they didn't ask for
• There's no way to configure this behavior — neither in the extension settings nor in VS Code's built-in settings

Current behavior

1. User is working in a single editor group with Claude Code open as a tab
2. Claude Code triggers a review (plan approval, diff view, etc.)
3. The review opens in a new editor group to the right (or bottom, depending on workbench.editor.openSideBySideDirection)
4. Screen is now split — user has to manually close the extra group every time

Expected behavior

A new extension setting (e.g., claudeCode.reviewLocation or claudeCode.openDiffsInActiveGroup) that allows users to choose:

• "beside" (current default) — opens review in a new editor group
• "active" — opens review in the current/active editor group as a regular tab

Technical context

The extension uses ViewColumn.Beside when calling vscode.diff or createWebviewPanel for review views. The fix would be to check a configuration setting and use ViewColumn.Active instead when the user prefers it.

Similarly, createPanel() in the extension defaults to ViewColumn.Beside for new Claude Code tabs. The claude-vscode.primaryEditor.open command already supports ViewColumn.Active — this behavior should be configurable as the default.

Environment

• VS Code on Windows 11
• Claude Code extension v2.1.83