Fix eval query path regressed by cleanup (results/ → eval/)

The eval route was looking for queries.yaml under data_dir/results/
after Qwen's cleanup, but the spec (test + README layout) places it
at data_dir/eval/. Restores the documented path and unbreaks
test_run_eval_keeps_its_files_on_the_data_volume_and_reports_status.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G9K7DZE8v1AYvfKU4qrQN5

src/mdmem/ui/app.py

@@ -627,7 +627,7 @@ def build_ui_app(svc: MemoryService) -> FastAPI:  # noqa: C901 - one place, many
         from mdmem.evalharness import run_eval_cli
 
         data_dir = settings.index_db.parent
-        queries = data_dir / "results" / "queries.yaml"
+        queries = data_dir / "eval" / "queries.yaml"
         if not queries.exists():
             # §11: a run needs 50-100 labelled queries. Say so on the page
             # instead of starting a job that prints a hint into the log and