Add option to hide vi mode indicator while keeping vi mode active

Summary

When vi mode is enabled, Claude Code displays a --INSERT-- / --NORMAL-- indicator. There is currently no way to hide this indicator without disabling vi mode entirely.

Problem

Many users who enable vi mode also configure a custom statusline that already displays the current vi mode (via the vim.mode field in the statusline JSON). In that case, the built-in --INSERT-- / --NORMAL-- indicator becomes redundant — it duplicates information that's already visible in the statusline.

There should be an option to hide the vanilla mode indicator while keeping vi mode active, so users who prefer the statusline version aren't stuck with two indicators showing the same thing.

Proposed Solution

A setting such as "viModeIndicator": false (or similar) that controls the visibility of the built-in mode indicator independently from whether vi mode itself is enabled.

Use Case

1. User enables vi mode via /vim or /config
2. User configures a custom statusline that includes vim.mode
3. User sets "viModeIndicator": false to hide the redundant built-in indicator
4. Vi keybindings remain fully functional, mode is shown only in the statusline