Add Restocking tab with budget-aware order recommendations

[upen7]

Summary

• Adds a new Restocking tab with a $1K–$100K budget slider that auto-selects demand-forecasted items greedily within budget. Users can adjust quantities, deselect items, and submit an order.
• Adds three backend endpoints — recommendations (demand × cost), POST/GET restocking orders — with a fixed 7-day delivery lead time.
• Submitted restocking orders now appear in a new highlighted section at the top of the Orders tab with the estimated delivery date.
• Adds an interactive architecture page at docs/architecture.html and a Coding Standards note in CLAUDE.md.

Changes

Frontend

• client/src/views/Restocking.vue — new view (budget slider, recommendations table, place-order flow)
• client/src/views/Orders.vue — new "Submitted Restocking Orders" section pinned at top
• client/src/main.js — registers /restocking route
• client/src/App.vue — adds Restocking nav link
• client/src/api.js — 3 new client methods

Backend

• server/main.py — GET /api/restocking/recommendations, POST /api/restocking-orders, GET /api/restocking-orders, Pydantic models, fallback unit-cost map

Docs

• docs/architecture.html — interactive system architecture page
• CLAUDE.md — Coding Standards section

Test plan

• Frontend loads at /restocking
• Budget slider + number input syncs both directions, clamps to $1K–$100K
• Recommendations sorted by forecasted demand desc
• Auto-select picks items greedily within budget
• Reducing the budget trims overflow selections
• "Place Order" POSTs and clears the selection with success toast
• Submitted orders appear at top of Orders tab with 7-day delivery date
• All 7 nav tabs load without errors (verified via Playwright)

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