muxr v3.5.0 Companion panes: an optional review/preview pane beside the runtime, created at launch and faithfully recreated on restore (ADR 0004). - feat: companion pane at the create_session chokepoint. Opt-in, config-driven ([companion] global, or [repos.<name>.companion] override); recreated on launch, recycle, and local restore with no state.json change; focus stays on the runtime. - docs: ADR 0004 flipped to Accepted (implemented).