Clarify diagnostic language and explanations

tests/test_web.py

@@ -23,6 +23,8 @@ def test_web_analysis_uses_production_health_pipeline(tmp_path):
     assert result["smart_crates"] == 2
     assert result["database_entries"] == 10
     assert result["database_library_matches"] == 10
+    assert result["database_missing_paths"] == 0
+    assert result["database_missing_unique_filenames"] == 0
     assert result["tracks_missing_from_database"] == 0
 
 
@@ -36,3 +38,7 @@ def test_web_static_assets_are_declared_and_packaged():
 
     assert set(STATIC_FILES) == {"/", "/app.css", "/app.js"}
     assert all((asset_root / filename).is_file() for filename, _ in STATIC_FILES.values())
+    html = (asset_root / "index.html").read_text(encoding="utf-8")
+    assert "Missing tracks in Serato" in html
+    assert "Old crate references" in html
+    assert html.count('class="info-button"') >= 10