feat: demo CORS, demo client, openpyxl catalog load

- Load consumable catalog XLSX with openpyxl and drop the pandas dependency.
- Add optional demo CORS settings and FastAPI CORSMiddleware for browser clients.
- Add scripts/demo_client static page and local server for API smoke tests.

Made-with: Cursor

pyproject.toml

@@ -12,7 +12,6 @@ dependencies = [
     "fastapi>=0.136.0",
     "loguru>=0.7.3",
     "openpyxl>=3.1.5",
-    "pandas>=2.3.0",
     "pillow>=12.2.0",
     "pydantic-settings>=2.13.1",
     "python-multipart>=0.0.26",