Add Restocking view with budget optimizer

[VZhuck]

Summary

• New Restocking page with a budget slider and greedy algorithm that auto-selects items maximizing demand coverage within the available budget
• POST /api/restocking-orders backend endpoint that creates RST-YYYY-NNNN orders and appends them to the in-memory orders list
• Orders view gains a "Submitted Restocking Orders" section showing RST orders with expandable item detail rows
• Wired /restocking route, nav link (with i18n), and createRestockingOrder API call
• Updated demand_forecasts.json and added Playwright MCP config (token replaced with env-var placeholder)

Test plan

• Start backend (uv run python main.py) and frontend (npm run dev)
• Navigate to Restocking page — items table loads with greedy pre-selection
• Move budget slider — selection updates automatically to stay within budget
• Toggle individual checkboxes — remaining budget updates in real time
• Click Place Order with items selected — success banner shows order number
• Navigate to Orders page — submitted RST order appears in the new section
• Verify warehouse/category filters reload the restocking table correctly

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