feat(paths): confetti for a finished path, and an import's progress

Finishing a path bursts confetti over the view saying so: pieces in the
palette's brightest colours fall once from the top, turning, and fade
out in under two seconds, so the screen settles. Drawn by hand rather
than with a package; nothing falls with animations switched off on the
device.

Importing paths into a studyset shows its Paths tab at once, and above
the paths, as they come in, how far the import has come: which path of
how many, by its title, and a bar filling with every path and step
stored. Before, the paths appeared one by one in whatever tab showed,
with nothing saying how many were still to come.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -400,6 +400,28 @@ class AppLocalizationsDe extends AppLocalizations {
     return '$file konnte nicht importiert werden. $reason';
   }
 
+  @override
+  String pathImportReading(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: '$count Dateien werden gelesen …',
+      one: 'Datei wird gelesen …',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String pathImportStoring(int index, int count, String title) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'Pfad $index von $count wird importiert: „$title“ …',
+      one: '„$title“ wird importiert …',
+    );
+    return '$_temp0';
+  }
+
   @override
   String pathsImported(int count, int steps) {
     String _temp0 = intl.Intl.pluralLogic(