feat: optimize background tasks and fix warehouse pricelist workflow

Optimize task retention from 5 minutes to 30 seconds to reduce polling overhead since toast notifications are shown only once. Add conditional warehouse pricelist creation via checkbox. Fix category storage in warehouse pricelists to properly load from lot table. Replace SSE with task polling for all long operations. Add comprehensive logging for debugging while minimizing noise from polling endpoints.

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

internal/models/pricelist.go

@@ -55,6 +55,7 @@ type PricelistItem struct {
 	ID          uint    `gorm:"primaryKey" json:"id"`
 	PricelistID uint    `gorm:"not null;index:idx_pricelist_lot" json:"pricelist_id"`
 	LotName     string  `gorm:"size:255;not null;index:idx_pricelist_lot" json:"lot_name"`
+	LotCategory *string `gorm:"column:lot_category;size:50" json:"category,omitempty"`
 	Price       float64 `gorm:"type:decimal(12,2);not null" json:"price"`
 	PriceMethod string  `gorm:"size:20" json:"price_method"`
 
@@ -65,10 +66,9 @@ type PricelistItem struct {
 	MetaPrices       string   `gorm:"size:1000" json:"meta_prices,omitempty"`
 
 	// Virtual fields for display (not stored in qt_pricelist_items table)
-	// LotDescription and Category are populated via JOIN in SQL queries
-	// AvailableQty and Partnumbers are populated programmatically
+	// LotDescription is populated via JOIN in SQL queries
+	// AvailableQty and Partnumbers are populated programmatically for warehouse pricelists
 	LotDescription string   `gorm:"-" json:"lot_description,omitempty"`
-	Category       string   `gorm:"-" json:"category,omitempty"`
 	AvailableQty   *float64 `gorm:"-" json:"available_qty,omitempty"`
 	Partnumbers    []string `gorm:"-" json:"partnumbers,omitempty"`
 }