[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.

Start in selection.lua and reproduce the setup with terminal.provider = "none" and sidekick.nvim using the tmux backend. Check how the terminal buffer is identified and verify that selecting it retains the last active code buffer instead. Confirm the fix with the described reproduction steps.

Vom Indexierungsmodell aus dem Issue-Text verfasst.