perf(startup): paint a splash immediately, run init off the first frame

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.

apps/app_seeds/lib/i18n/pt.i18n.json

@@ -2,6 +2,10 @@
   "app": {
     "title": "Tanemaki"
   },
+  "bootstrap": {
+    "failed": "O Tanemaki não conseguiu iniciar",
+    "retry": "Tentar de novo"
+  },
   "common": {
     "save": "Guardar",
     "cancel": "Cancelar",