rememberNutrientToolbarCoordinator

Composable-scoped binding for ToolbarCoordinator.

Use this when:

• You're writing a Compose-only screen that hosts com.pspdfkit.ui.PdfFragment via AndroidFragment {}.

• You're in the compose-flavor DocumentContainer.

• You're writing a Compose preview / test that needs a real coordinator.

State (frame visuals + per-item enabled/selected/visible bits) is persisted via rememberSaveable so it survives configuration changes and process death. Action lambdas are not persisted — producers must re-register them on the restored coordinator (ADR-Toolbar-4). See STATE-2b.

Cleanup happens automatically when this composable leaves the composition tree, via DisposableEffect.

Pre-Phase 0 scaffolding (ADR-Toolbar-3, factory 3 of 3).