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/test/ui/bootstrap_splash_test.dart

@@ -0,0 +1,33 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/bootstrap.dart';
+import 'package:tane/i18n/strings.g.dart';
+
+void main() {
+  setUp(() => LocaleSettings.setLocaleSync(AppLocale.en));
+
+  testWidgets('shows a spinner and no error while booting', (tester) async {
+    await tester.pumpWidget(
+      TranslationProvider(child: const BootstrapSplash(error: false)),
+    );
+
+    expect(find.byType(CircularProgressIndicator), findsOneWidget);
+    expect(find.text(t.bootstrap.failed), findsNothing);
+    expect(find.text(t.bootstrap.retry), findsNothing);
+  });
+
+  testWidgets('on error shows the message and a working retry', (tester) async {
+    var retries = 0;
+    await tester.pumpWidget(
+      TranslationProvider(
+        child: BootstrapSplash(error: true, onRetry: () => retries++),
+      ),
+    );
+
+    expect(find.byType(CircularProgressIndicator), findsNothing);
+    expect(find.text(t.bootstrap.failed), findsOneWidget);
+
+    await tester.tap(find.text(t.bootstrap.retry));
+    expect(retries, 1);
+  });
+}