Clears the remaining no-unused-vars warnings across the dashboard app and
server, desktop main, and engine sources. Dead React state destructures are
collapsed to setter-only, unused props are underscore-prefixed to preserve
API shape, and unreferenced catch bindings are dropped. No behaviour change.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
- Add preview embed diagnostics with richer error classification and fallback state handling
- Improve PreviewIframe and DevServerView retry UX for timeout and iframe failure states
- Adjust preview layout/styles to prevent clipping and header overflow while keeping fallback panels centered
- Expand dashboard tests to cover fallback transitions, retry flows, and responsive CSS behavior
- Add usePreviewEmbed hook to derive preview embed URLs and availability state
- Add PreviewIframe component with iframe load/error wiring and deduplicated error callbacks
- Integrate preview panel actions, fallback messaging, and embedded iframe rendering in DevServerView
- Expand test coverage for usePreviewEmbed, PreviewIframe, and DevServerView preview integration scenarios