Add Mago4 demo ERP with Python FastAPI

Implements a working in-memory ERP demo inspired by Mago4, covering
the core modules: dashboard with KPI widgets, customers, suppliers,
products, sales orders, purchase orders, and warehouse inventory.

- FastAPI backend with Pydantic models and REST API (auto-docs at /docs)
- Jinja2 HTML templates with Mago4-style UI (dark sidebar, blue/orange/
  green/red palette, Material Design icons)
- In-memory fake database seeded with sample customers, suppliers,
  products, and orders — ready to swap for SQLAlchemy + SQL Server
- Workarounds for Python 3.14 + Starlette 1.3 / Jinja2 compatibility
  (cache_size=0, new TemplateResponse(request, name, ctx) signature)
- launch.json for one-click preview; run.bat for manual startup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

run.bat

@@ -0,0 +1,29 @@
+@echo off
+REM Mago4 Demo - Script di avvio
+
+echo.
+echo ╔════════════════════════════════════════════════════════════╗
+echo ║         Mago4 Demo - ERP Gestionale (FastAPI)             ║
+echo ╚════════════════════════════════════════════════════════════╝
+echo.
+
+REM Verificare se Python è installato
+python --version >nul 2>&1
+if errorlevel 1 (
+    echo [ERRORE] Python non trovato. Installare Python 3.8+
+    exit /b 1
+)
+
+echo [1] Controllo dipendenze...
+pip install -r requirements.txt
+
+echo.
+echo [2] Avvio applicazione...
+echo.
+echo Dashboard disponibile su: http://127.0.0.1:8000
+echo API Documentation su:     http://127.0.0.1:8000/docs
+echo.
+echo Premi CTRL+C per fermere il server
+echo.
+
+python main.py