feat(js): add View JS object for main-view automation + screenshots

[edumeneses]

What

Adds a new View JavaScript object (JsViewContext) that exposes the main
scenario view to scripting — enabling automation of the editor for tasks like
generating documentation screenshots. It is a sibling of the existing Score
(EditContext) and Util objects.

API (all methods no-op when there is no GUI, e.g. --no-gui)

Screenshots

• View.grabScene(path) — render the scenario scene to SVG (vector), reusing the F10 snapshot code path
• View.grabMainWindow(path) — grab the main window (with chrome) → raster (PNG by extension)
• View.grabScreen(path) — grab the whole screen, all windows → raster

Viewport / navigation

• View.zoom(zx, zy), View.scroll(dx, dy), View.setZoomRatio(r)
• View.centerOn(process) — focus the view on a given ProcessModel, resolving its on-screen item in both nodal (NodeItem) and temporal (layer) modes
• View.goToInterval(interval), View.fit(), View.recenter()

Mode

• View.setNodal(bool) / View.isNodal() — switch between temporal and dataflow modes

zoom/scroll are also kept on Score as aliases (non-breaking).

How

• SnapshotAction: the scene→SVG logic is extracted into an exported, reusable
  Scenario::renderSceneToSvg(scene, path, rect) so the F10 action and
  View.grabScene() share one code path (F10 behavior unchanged).
• ScenarioDocumentPresenter: adds public setNodalMode() / recenter()
  wrappers so the view-control functionality is reachable from the JS object.
  Mode switching routes through the toolbar action so its checked state stays in sync.
• JsViewContext reaches the document/view/presenter via
  GUIAppContext().currentDocument(), a viewDelegate() cast, and
  IDocument::try_presenterDelegate<ScenarioDocumentPresenter>() (returns null
  headless → methods no-op). Registered as View on the console and script-UI engines.

Testing

• Builds clean (scenario + js plugins compile and link).
• Verified in a live GUI console: View.grabScene() produced a valid 79 KB SVG,
  View.grabMainWindow() a 1882×2085 PNG, and View.isNodal() returned the
  expected value.

🤖 Generated with Claude Code