Add triage tests, prepare-export, and UI fixes for Levkin migration.

Cherry-pick heuristics, manifest merge, global file search, scrollbar styling, and pytest/Playwright coverage unblock review and filtered export for mmetl.

tests/test_slack_export.py

@@ -0,0 +1,58 @@
+"""Unit tests for slack_export.py (mini-export fixture)."""
+
+from __future__ import annotations
+
+
+def test_fixture_has_expected_channels(export):
+    names = {c["name"] for c in export.build_summary()["channels"]}
+    assert names >= {"medical", "zoey", "153niagara"}
+
+
+def test_normalize_message_shape(export):
+    msgs = export.iter_channel_messages("medical")
+    msg = msgs[0]
+    assert "id" in msg
+    assert "channel" in msg
+    assert msg["channel"] == "medical"
+    assert "user_name" in msg
+    assert "text" in msg
+
+
+def test_classify_file_types(export):
+    assert export.classify_file({"name": "lease.pdf", "mimetype": "application/pdf"}) == "pdf"
+    assert export.classify_file({"name": "photo.jpg", "mimetype": "image/jpeg"}) == "image"
+    assert export.classify_file({"name": "data.xlsx", "mimetype": ""}) == "spreadsheet"
+
+
+def test_search_channels(export):
+    hits = export.search_channels("med")
+    assert any(c["name"] == "medical" for c in hits)
+    assert not any(c["name"] == "zoey" for c in hits)
+
+
+def test_search_global_text(export):
+    result = export.search_global("doctor", limit=20)
+    assert result["query"] == "doctor"
+    assert isinstance(result["messages"], list)
+
+
+def test_search_files_global_images(export):
+    result = export.search_files_global("", file_type="image", limit=30)
+    assert result["file_type"] == "image"
+    for hit in result["hits"]:
+        kinds = set(hit.get("file_kinds") or [])
+        assert "image" in kinds
+
+
+def test_channel_messages_all_sorted(export):
+    data = export.channel_messages_all("zoey")
+    assert data["channel"] == "zoey"
+    assert data["total"] == len(data["messages"])
+    times = [m.get("time") or "" for m in data["messages"]]
+    assert times == sorted(times)
+
+
+def test_upload_path_safe(export):
+    rel = export.upload_relpath("F123", "my file.pdf")
+    assert rel == "__uploads/F123/my file.pdf"
+    assert ".." not in rel