[BUG] Hardcoded terminal buffer filter breaks with external terminal setups

## Bug Description

The terminal buffer filter in `selection.lua` is hardcoded to only match buffers containing "claude" in their name. When Claude Code runs via sidekick.nvim with `mux.backend = "tmux"`, the terminal buffer is named `term://...tmux` - it never contains "claude". As a result, selection tracking treats the tmux terminal as an active code buffer instead of ignoring it.

I have a fix ready and will open a PR shortly.

## To Reproduce

1. Configure claudecode.nvim with `terminal.provider = "none"`
2. Launch Claude Code via sidekick.nvim with tmux backend
3. Switch cursor to the Claude Code terminal pane
4. Selection tracking reports the tmux terminal buffer instead of the last active code file

## Expected Behavior

Selection tracking should ignore the terminal buffer and retain the last active code buffer, regardless of how Claude Code was launched.

## Environment

n/a - the issue is in the Lua filter logic, independent of versions.

## Error Messages

No error messages. The filter silently fails to match.

selection.lua から始め、tmux バックエンドの sidekick.nvim と terminal.provider = "none" を使ってセットアップを再現します。ターミナルバッファがどのように識別されるかを確認し、それを選択した場合に、代わりに最後にアクティブだったコードバッファが保持されることを検証します。説明されている再現手順で修正を確認します。

索引モデルが issue の本文から書いたものです。