Adds POST /api/cafes/{cafeId}/demo/seed (owner-only) that seeds:
- 9% default VAT tax
- 7 menu categories + 59+ items via DemoMenuSeeder
- 15 inventory ingredients (coffee shop staples)
- 10 tables across 3 floors on the first active branch
Frontend DemoDataBanner appears on menu, tables, and inventory
pages when the café is completely empty, so owners can populate
demo data in one click instead of entering everything manually.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
soroush.asadi