Add Restocking tab with budget-driven demand forecast recommendations

[ryan-weidinger]

Summary

• New Restocking tab (/restocking) with a budget slider ($10K–$500K) that greedily recommends items from demand forecasts — increasing-trend items first, then stable; decreasing items excluded
• Backend endpoint POST /api/restocking/orders creates an internal order with a 14-day delivery lead time and is_restocking_order: true flag
• Orders tab gets a new "Submitted Restocking Orders" section (blue left border) that surfaces RST- orders separately; stat cards and status filters operate only on regular customer orders so counts are unaffected
• Data fix: replaced fictional SKUs in demand_forecasts.json (WDG-001, BRG-102, etc.) with real inventory SKUs (PCB-001, PCB-002, TMP-201, PRS-203, HMD-202, ULS-205, PRX-204, SRV-301, SRV-302) so the recommendation algorithm can join on unit cost
• Full EN/JA i18n coverage for all new strings
• Architecture doc added at docs/architecture.html

Test plan

• Navigate to Restocking tab — budget slider defaults to $100K, 7 items recommended, total ~$98,233
• Move slider to $20K — only PCB-001 fits ($12,495 line cost)
• Move slider to $10K — empty state: "No items fit within the current budget"
• Click "Place Restocking Order" — success message appears
• Navigate to Orders tab — "Submitted Restocking Orders" section shows the RST- order with expected delivery 14 days out
• Confirm stat cards (Processing/Shipped/etc.) are unchanged by the restocking order
• Expand the order's items dropdown — all line items visible
• Switch to Japanese locale — all new strings render in Japanese

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