[FEATURE] Add Vim mode to custom status line configuration

Bug Description
Feature Request: Include Vim mode in custom status line

When using Vim mode with a custom status line (via statusLine in settings.json), two lines are displayed:

1. Custom status line
2. Built-in Vim mode indicator (-- INSERT --)

Request:

1. Add vim_mode string to status line JSON (e.g., "vim_mode": "insert")
2. Add setting to hide the built-in indicator (e.g., "showVimModeIndicator": false)

This would let users display everything on a single line.

Example of current output

<img width="399" height="97" alt="Image" src="https://github.com/user-attachments/assets/137dfb51-41f0-4771-a6c4-c6e06ef819c2" />

Environment Info

• Platform: darwin
• Terminal: tmux
• Version: 2.1.12
• Feedback ID: 16754f16-2f72-49b1-9eec-fbf04d137b69