Release v4.31.0

A new package, @cratis/scene.preview, holds the one host a design tool mounts to let an author click around the application as an end user would - and the one composition Stage shares. ScenePreviewHost renders the effective application from an in-memory document with sample data and a dry-run invoker.

Added

• ScenePreviewHost({ document, structure, navigation, target, sampleData, registry, invoker, ... }): a module target renders the application shell with the module's effective navigation and its first feature, a feature target that feature in the shell, a State Change slice target its task dialog over a minimal host page (the feature's own page when it has one), a State View slice target its data fragment. Navigation keeps to an in-memory history, so a preview never touches the hosting page's address, and going to another module swaps the effective navigation (effectiveNavigation, not re-implemented). It reports onBreadcrumbChange (Sales › Orders) and calls onExit on Escape when no dialog is open - the strip itself is the embedding application's.
• Read-only and never blank (PRV8): diagnosePreview judges the model with the engine's own validators and returns PreviewProblem entries (code, severity, message, nodeId). Errors (targetNotFound, moduleWithoutFeatures, sliceNotPreviewable, screenMissing, layoutMissing, templateMissing, templateUnplaced) replace the render with a problem list; warnings (structureInvalid, navigationInvalid, toolbarInvalid, sampleDataInvalid, sliceFragmentMissing) are reported and the preview renders. onProblems and onSelectProblem are the host's hooks.
• Dry run (PRV5): a submitted dialog validates and sends nothing; a toast says "Command would be sent" with the payload in an expandable detail. A real invoker can be passed instead.
• Sample data (PRV6): createPreviewSampleData asks resolveSampleData - bound pack, the application profile's active pack, the blueprint's default pack, generated data - for the queries the document binds and the commands its slices accept; sessionActivePack is the strip's session-only override of the profile's choice. The same seed gives the same rows.
• One composition for preview and Stage (PRV9, REN2): composeApplicationScreen (shell, chrome, the screen inside its template chain with every arrangement applied, name resolution, effective configuration), composeOutletScreen, composeDialog, collectDestinations, previewProfile, and ApplicationHost, which runs it - shell, nested outlets, navigation regions, routes and dialogs. A host decides only what is its own through CompositionOptions and renderScreen. The template wrapper (Scene:template) and the flow arrangement view Stage kept to itself now live here, so Stage can delete its copies.
• SliceCommandField.initialValue: a task dialog's field can start with a value - a preview fills it from the active sample data pack.
• Docs: Documentation/blueprints/preview-host.md.

Part of #106