Fix .gitignore 'plugins/' rule that was accidentally ignoring source
files in v2/src/lib/plugins/. Narrow to /plugins/ and /v2/plugins/
(runtime plugin directories only). Track plugin-host.ts (was written
but never committed) and add comprehensive test suite covering all 13
shadowed globals, this-binding, permission gating, API freeze, and
lifecycle management.
Create Cargo workspace at v2/ level with members: src-tauri,
bterminal-core, bterminal-relay. Extract PtyManager and SidecarManager
into shared bterminal-core crate with EventSink trait for abstracting
event emission. TauriEventSink wraps AppHandle. src-tauri pty.rs and
sidecar.rs become thin re-exports. Move Cargo.lock to workspace root.
Add v2/target/ to .gitignore.
