JSON output no longer escapes non-ASCII characters, new --ascii option (#777)

Closes #625

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JaHan1NhaTRAxJ9LQtSLf9

tests/test_cli_convert.py

@@ -215,6 +215,25 @@ def test_convert_multi_dryrun(test_db_and_path):
     )
 
 
+def test_convert_multi_dryrun_unicode_not_escaped(test_db_and_path):
+    db_path = test_db_and_path[1]
+    result = CliRunner().invoke(
+        cli.cli,
+        [
+            "convert",
+            db_path,
+            "example",
+            "dt",
+            "{'text': 'Japanese 日本語'}",
+            "--dry-run",
+            "--multi",
+        ],
+    )
+    assert result.exit_code == 0
+    # Preview should match what jsonify_if_needed() would actually store
+    assert '{"text": "Japanese 日本語"}' in result.output
+
+
 @pytest.mark.parametrize("drop", (True, False))
 def test_convert_output_column(test_db_and_path, drop):
     db, db_path = test_db_and_path