Add RAGAS evaluation web console (FastAPI + vanilla JS)

- webapp/: FastAPI backend with runs/scenarios/evaluations API routers;
  services for run_reader, report_builder, scenario_scanner, task_manager
  (lazy ragas import — server boots even without ragas); Pydantic models
- webapp/static/: single-page console (layout A: left-nav + main area);
  report detail with metric cards, Chart.js distribution histogram,
  grouping table, lowest-score sample review; trigger evaluation + log polling
- webmain.py: uvicorn entry point (alongside existing main.py CLI)
- start.bat: Windows one-click launcher with env checks and auto-browser open
- rag_eval/datasets/: implement missing loader + normalizer modules
  (load_dataset_records, normalize_records) required by evaluator
- scripts/seed_sample_run.py: generate realistic demo run artifacts
- .gitignore: exclude datasets/ data files but keep rag_eval/datasets/ source

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

webapp/server.py

@@ -0,0 +1,49 @@
+"""FastAPI application factory for the RAGAS evaluation console.
+
+The app mounts three JSON API routers and serves the single-page static
+frontend. It imports rag_eval only lazily (inside the task manager worker), so
+the server starts even when the evaluation dependencies are not yet installed.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from fastapi import FastAPI
+from fastapi.responses import FileResponse
+from fastapi.staticfiles import StaticFiles
+
+from webapp.api import evaluations, runs, scenarios
+
+STATIC_DIR = Path(__file__).resolve().parent / "static"
+
+
+def create_app() -> FastAPI:
+    """Build and configure the FastAPI application instance."""
+    app = FastAPI(
+        title="Siemens RAGAS 评估控制台",
+        description="RAGAS 评估子系统的可视化报告与评估触发控制台。",
+        version="0.1.0",
+    )
+
+    app.include_router(runs.router)
+    app.include_router(scenarios.router)
+    app.include_router(evaluations.router)
+
+    @app.get("/api/health", tags=["meta"])
+    def health() -> dict[str, str]:
+        """Report basic liveness so the UI can confirm the server is reachable."""
+        return {"status": "ok"}
+
+    @app.get("/", include_in_schema=False)
+    def index() -> FileResponse:
+        """Serve the single-page console entry document."""
+        return FileResponse(STATIC_DIR / "index.html")
+
+    # Serve CSS/JS assets under /static while keeping API routes at /api.
+    app.mount("/static", StaticFiles(directory=STATIC_DIR), name="static")
+
+    return app
+
+
+app = create_app()