fix(search): fix _toFtsQuery to split on non-word chars instead of stripping

The old implementation stripped non-word chars within tokens, causing
'searchable-{timestamp}' to become 'searchable{timestamp}*'. FTS5
tokenizes on hyphens so the merged token never matched.

Fix: split on [^\w]+ so each FTS token is queried separately.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/repositories/email_repository_impl.dart

@@ -2992,9 +2992,7 @@ class EmailRepositoryImpl implements EmailRepository {
   static String _toFtsQuery(String query) {
     final words = query
         .trim()
-        .split(RegExp(r'\s+'))
-        .where((w) => w.isNotEmpty)
-        .map((w) => w.replaceAll(RegExp(r'[^\w]'), ''))
+        .split(RegExp(r'[^\w]+'))
         .where((w) => w.isNotEmpty)
         .toList();
     if (words.isEmpty) return '';