The pre-init BootstrapSplash passed the raw device locale to its
MaterialApp, so booting under an Asturian (ast) device locale threw
the 'locale not supported by localization delegates' warning — the
Material/Cupertino delegates ship no ast. The main app already routes
ast to Spanish framework chrome via materialLocaleFor; apply the same
mapping in the splash. Drop @visibleForTesting since it's now shared
production code.
main() awaited all of configureDependencies() (open the encrypted DB,
derive the social key, seed/scan the species catalog) before the first
runApp, so nothing painted until init finished — startup jank visible as
skipped frames. Now main() runs runApp immediately with a Bootstrap
widget that shows a native-splash-matching green splash while the heavy
work runs, then swaps in TaneApp. On failure it shows a localized error
with a retry (configureDependencies is idempotent, so retry is safe).
Adds a bootstrap i18n group (en/es/pt/ast) and a widget test for the
splash/error frame.
