[FEATURE] Allow A ClaudeCode-Per-Tab

## Feature Description
`:ClaudeCode` appears to only work in the current tab. This is somewhere between a bug and a feature request but basically people should be able to make at least one Window of ClaudeCode per-tab.

```vim
:tabnew
:ClaudeCode
:tabnew
:ClaudeCode
```
(Creates 2 separate windows)

Currently if you try to Neovim tabs give a different view for buffers (e.g. `:tabnew`). Currently if you call `:ClaudeCode`, it
A clear and concise description of what you'd like to see added to the plugin.

## Use Case

Though I'd love to just use tmux, it's not always available. When that happens, I use Neovim tabs.

And just in general being able to have more than one Claude Code open in a single Neovim instance would be generally useful

## Proposed Solution

If a new command like `:ClaudeCodeFromThisWindow` or something was created, I could manage the windows myself programmatically.

## Alternatives Considered

Possibly related: https://github.com/coder/claudecode.nvim/issues/187

:ClaudeCode コマンドから始め、この issue の :tabnew の例全体でその動作を比較し、続いて関連する issue 187 を確認します。完了の条件は、分離された Neovim タブがそれぞれ独立した Claude Code ウィンドウを作成・管理できることです。これは、:ClaudeCode を繰り返し呼び出す方法でも、:ClaudeCodeFromThisWindow のようなコマンドを使う方法でも構いません。

索引モデルが issue の本文から書いたものです。