refactor: separate LOT management to dedicated page

- Create new /lot page with two tabs:
  1. LOT: component management (formerly in /admin/pricing)
  2. Сопоставления: partnumber ↔ LOT mappings (formerly in Warehouse tab)
- Remove LOT tab from Pricing Admin page
- Remove stock mappings section from Warehouse tab
- Update main menu: LOT link now points to /lot
- Default tab in Pricing Admin changed to Estimate
- Add Lot() handler in web.go
- Add /lot route in main.go

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

cmd/pfs/main.go

@@ -542,6 +542,7 @@ func setupRouter(cfg *config.Config, configPath string, connMgr *db.ConnectionMa
 	})
 
 	router.GET("/", webHandler.Index)
+	router.GET("/lot", webHandler.Lot)
 	router.GET("/pricelists", webHandler.Pricelists)
 	router.GET("/pricelists/:id", webHandler.PricelistDetail)
 	router.GET("/admin/pricing", webHandler.AdminPricing)