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>

config.ini

@@ -0,0 +1,29 @@
+# Mago4 Demo Configuration
+# Questo file può essere usato per estendere la configurazione
+
+[Database]
+TYPE=in-memory
+# Per SQL Server: mssql+pyodbc://user:password@server/dbname?driver=ODBC+Driver+17+for+SQL+Server
+# Per PostgreSQL: postgresql://user:password@localhost/dbname
+# Per SQLite: sqlite:///./mago4.db
+
+[Server]
+HOST=127.0.0.1
+PORT=8000
+DEBUG=True
+RELOAD=True
+
+[Features]
+ENABLE_AUTH=False
+ENABLE_PDF_EXPORT=False
+ENABLE_EMAIL_NOTIFICATIONS=False
+ENABLE_MULTICOMPANY=False
+
+[Pagination]
+DEFAULT_PAGE_SIZE=20
+MAX_PAGE_SIZE=100
+
+[Validation]
+MIN_CREDIT_LIMIT=1000
+MIN_PAYMENT_TERMS=1
+MAX_REORDER_QUANTITY=10000