[FEATURE] autocmd event to set up keybinds on the buffer

## Feature Description

I want an autocmd User event for addding specific keybind on the claude code buffer.

## Use Case

I want to toggle claudecode buffer with some keymap when the mode is terminal insert mode.

## Proposed Solution

ugaterm.nvim has this feature.

https://github.com/uga-rosa/ugaterm.nvim/commit/c12135abec935e2b78e99d710bbe9c7a690ab36e

With this event, I can add autocmds like this, and can close ugaterm buffer from terminal insert mode with just hitting ``.

```lua
vim.api.nvim_create_autocmd('User',
{
pattern = 'UgatermEnter',
callback =
function(args)
vim.keymap.set('t', '', '', { buffer = args.buf })
vim.keymap.set('n', '', 'UgatermHide', { buffer = args.buf })
end
})
```

Start by reviewing the plugin's existing Claude Code buffer setup and the proposed ugaterm.nvim commit linked in the issue. Identify where the buffer is created or entered, add the requested User autocmd behavior there, and verify that buffer-local terminal and normal-mode keymaps can be registered through the shown callback pattern.

索引モデルが issue の本文から書いたものです。