Guard editor-only DOM access in view setup

[tracygardner]

Motivation

• Prevent runtime errors when the app is embedded or served as standalone pages that lack editor DOM elements like codePanel or maincontent.
• Make UI initialization and view toggling robust on narrow/wide screens and in PWA/fullscreen contexts.
• Ensure canvas resizing and play/design mode flows do nothing when required UI elements are absent to avoid null dereferences.

Description

• Add null checks for DOM lookups in resizeCanvas, switchView, showCodeView, showCanvasView, togglePlayMode, addButtonListener, addSwipeListeners, setupViewObserver, and initializeUI and return early when required elements are missing.
• Guard accesses to optional elements such as gizmoButtons, fullscreenToggle, switchViewsBtn, bottomBar, flocklink, and maincontent before modifying styles or text content.
• Replace some transform-based view switching with DOM-based show/hide logic and ensure Blockly.svgResize is called only when workspace is present.
• Keep existing behavior for narrow/wide screen flows while making all UI-only operations safe on pages without the editor containers.

Testing

• No automated tests were run for this change.

---

Codex Task