854c854033
- Reworked Linux clipboard writes to use a shared `OnceLock<Mutex<Option<Clipboard>>>` so a `Clipboard` instance persists for the process and keeps X11 ownership alive. - Updated `copy_to_clipboard` to route Linux calls through the persistent helper while macOS and Windows keep transient on-thread writes. - Added changelog entries for the native X11 clipboard fix and the AI default Anthropic model note. Fixes #2075