Extract duplicated sandbox protocol logic from NsitePreviewDialog and
Webxdc into a single SandboxFrame component. Shared utilities (MIME
types, base64, HTML injection, JSON-RPC types) move to src/lib/sandbox/.
Add configurable sandboxDomain to AppConfig so the iframe.diy domain
can be overridden via ditto.json, preparing for native Capacitor
implementations.
Strip unused console/navigation/error RPC from previewInjectedScript,
leaving only the /index.html path normalization.
Alex Gleason