Failures while the app loads left only the splash, with nothing to report. Handlers in public/boot.js now load before the module graph and replace the splash with an error page with copyable diagnostics and a report link, for module load errors, rejected startup, initial render errors and a 30-second timeout. A successful start cancels the timer.
The production build also rejects selected newer startup APIs and unsupported regex and import syntax. The original macOS 11 trigger remains unconfirmed.
Refs #2008
