feat(api,ui): in-product demo showcase page (#132)

README.md

@@ -86,6 +86,10 @@ runs=3 winner=seasonal_naive alias=demo-production wall_clock=87s
 See `scripts/run_demo.py` for the contract and `make help` for the
 related targets (`demo-quick` skips re-seeding; `demo-clean` wipes the DB first).
 
+**Try it in the browser:** with the backend and frontend running, open
+[`/showcase`](http://localhost:5173/showcase) and click **Run pipeline** — the
+same end-to-end flow streams live into the dashboard as status cards (no CLI).
+
 ### Frontend Setup
 
 8. **Install frontend dependencies**

app/features/demo/__init__.py

@@ -0,0 +1,19 @@
+"""Demo showcase slice.
+
+Drives the end-to-end forecasting pipeline in-process (via ``httpx.ASGITransport``)
+and streams per-step progress, powering the dashboard's Showcase page. This slice
+has no database table of its own -- it reads and writes only through the other
+slices' HTTP endpoints (precedent: ``analytics``, ``dimensions``).
+"""
+
+from app.features.demo.pipeline import run_pipeline
+from app.features.demo.routes import router
+from app.features.demo.schemas import DemoRunRequest, DemoRunResult, StepEvent
+
+__all__ = [
+    "DemoRunRequest",
+    "DemoRunResult",
+    "StepEvent",
+    "router",
+    "run_pipeline",
+]