Add Step 4 fallback: generate key from folder name

- SerieScanner: generate key from folder when no key/data files exist
- Handle edge cases: non-Latin characters, special symbols in folder names
- anime_service: expose loading_status and loading_error fields
- Update tests to match new fallback behavior

tests/unit/test_serie_scanner.py

@@ -552,8 +552,8 @@ class TestReadDataFromFile:
             assert result is not None
             assert result.key == "test-key"
 
-    def test_no_files_returns_none(self, mock_loader):
-        """Should return None when no key or data file exists."""
+    def test_no_files_returns_serie_with_generated_key(self, mock_loader):
+        """Should return Serie with generated key when no key or data file exists."""
         import tempfile
 
         with tempfile.TemporaryDirectory() as tmpdir:
@@ -562,7 +562,10 @@ class TestReadDataFromFile:
 
             scanner = SerieScanner(tmpdir, mock_loader)
             result = scanner._SerieScanner__read_data_from_file("Empty")
-            assert result is None
+            # Step 4 generates key from folder name when no files exist
+            assert result is not None
+            assert isinstance(result, Serie)
+            assert result.key == "empty"
 
 
 class TestReinit:
@@ -763,7 +766,7 @@ class TestDbLookupFallback:
             assert scanner.keyDict["rooster-fighter"].episodeDict == {1: [1, 2, 3]}
 
     def test_db_lookup_returns_none_folder_skipped(self, mock_loader):
-        """When db_lookup returns None, the folder is skipped with a warning."""
+        """When db_lookup returns None, Step 4 fallback generates key from folder name."""
         import tempfile
 
         with tempfile.TemporaryDirectory() as tmp_dir:
@@ -773,10 +776,11 @@ class TestDbLookupFallback:
             with patch.object(scanner, 'get_total_to_scan', return_value=1):
                 scanner.scan()
 
-            assert len(scanner.keyDict) == 0
+            # Step 4 generates key from folder name, so keyDict is not empty
+            assert len(scanner.keyDict) == 1
 
     def test_db_lookup_exception_skips_folder(self, mock_loader):
-        """When db_lookup raises, the folder is skipped gracefully."""
+        """When db_lookup raises, Step 4 fallback generates key from folder name."""
         import tempfile
 
         with tempfile.TemporaryDirectory() as tmp_dir:
@@ -786,7 +790,8 @@ class TestDbLookupFallback:
             with patch.object(scanner, 'get_total_to_scan', return_value=1):
                 scanner.scan()  # should not raise
 
-            assert len(scanner.keyDict) == 0
+            # Step 4 generates key from folder name, so keyDict is not empty
+            assert len(scanner.keyDict) == 1
 
     def test_db_lookup_warning_logged_when_no_files(
         self, mock_loader, caplog