Add restocking workflow with budget-based order placement

[Mukassir995]

Summary

• New /restocking route (Restocking.vue) lets users set a budget, review demand-forecast recommendations, and submit a restock order in one flow
• POST /api/restock-orders backend endpoint creates a Submitted order in memory with auto-incremented order number and 14-day lead time
• Orders view gains a Submitted stat card and a submitted-orders table showing lead time and line items
• Full i18n coverage added to English and Japanese locales
• Architecture doc and backend tests included

Test plan

• Navigate to /restocking - budget input and recommendations table render
• Adjust budget - item list updates to fit within budget
• Click Place Order - success banner appears, order shows in Orders view under Submitted
• Navigate to /orders - Submitted stat card increments and submitted-orders table appears
• POST /api/restock-orders returns a valid Order object with correct total and 14-day delivery
• Run uv run pytest tests/backend/test_restock_orders.py -v - all tests pass
• Toggle language to Japanese - all new strings display correctly

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