feat: openInNewTab should reuse existing tab group (viewColumn arg or setting)

Summary

Ctrl+Shift+Esc (anthropic.claude-code.openInNewTab) always opens Claude in a new tab group, with no way to configure it to reuse the existing one.

Desired behavior

One or both of:

1. Keybinding arg support — allow viewColumn to be passed so users can control placement:

``json
{
"key": "ctrl+shift+escape",
"command": "anthropic.claude-code.openInNewTab",
"args": { "viewColumn": "active" }
}
``

1. Setting — a claude.preferredTabGroup (or similar) that controls whether new tabs open beside the active editor or in a new group.

Why

Standard VS Code commands (e.g. vscode.open, workbench.action.splitEditor) accept viewColumn as a keybinding argument. Claude Code's command does not, so there is no keyboard-driven way to open a new Claude tab in the same group — every invocation fractures the layout.

Workaround today

None that fully works. openInSidebar keeps Claude in the panel (not a tab). Rebinding the key can focus an existing group but cannot prevent a new group from being created if no Claude tab is already active.

Environment

• Claude Code VS Code extension
• Linux (applies equally to Mac/Windows)