Allow configuring default scope for /resume session picker

Feature Request

Problem

When using /resume (or the session picker), the default view is always current directory (current worktree). Users who work with multiple worktrees frequently need to press A every time to switch to all projects view.

There is currently no way to configure this default behavior.

Proposed Solution

Add a configuration option in settings.json to control the default scope of the /resume session picker:

{
  "resumePickerDefaultScope": "all-projects"
}

Possible values:

• current-directory (current default behavior)
• ^Gll-projects (show all worktrees/projects)

Use Case

When working with git worktrees, the all projects view is far more useful as the default because:

1. You often want to resume a session started in a different worktree
2. Pressing A every time adds friction to the workflow
3. The current directory filter is too narrow for multi-worktree workflows

Workaround

Currently, the only workaround is to press A immediately after /resume to toggle to the all projects view.

Additional Context

The session picker already supports the A key toggle between views, so the infrastructure for both views exists. This request is simply about making the default configurable.