feat: rename project to 'Siemens RAGAS 评估平台' in frontend

- index.html: page title, brand-mark, brand-sub
- server.py: FastAPI app title
- app.css: comment header

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

webapp/server.py

@@ -87,7 +87,7 @@ OPENAPI_TAGS = [
 def create_app() -> FastAPI:
     """Build and configure the FastAPI application instance."""
     app = FastAPI(
-        title="RAGAS 评估系统",
+        title="Siemens RAGAS 评估平台",
         description=(
             "西门子医疗影像 RAG 评估平台 API 文档。\n\n"
             "提供以下能力：\n"