Show detailed batch repair preview

tests/test_web.py

@@ -60,6 +60,8 @@ def test_web_static_assets_are_declared_and_packaged():
     assert "Old crate references" in html
     assert "Choose a diagnostic" in html
     assert "Backup recovery" in html
+    assert "Here’s exactly what will happen" in html
+    assert 'id="batch-preview-modal"' in html
     assert 'data-detail="database_missing_tracks"' in html
     assert 'data-detail="old_crate_references"' in html
     assert html.count('class="info-button"') >= 10
@@ -139,4 +141,7 @@ def test_batch_preview_combines_approved_groups_without_changes(tmp_path):
     assert result["applied"] is False
     assert result["choice_count"] == 2
     assert len(result["replaced"]) == 2
+    assert len(result["decisions"]) == 2
+    assert result["decisions"][0]["keeper"].endswith("First.mp3")
+    assert len(result["decisions"][0]["replaced"]) == 1
     assert all(not Path(choice["group_files"][1]).is_symlink() for choice in choices)