feat: implement background task system with notifications

- Added background task manager with goroutine execution and panic recovery
- Replaced SSE streaming with background task execution for:
  * Price recalculation (RecalculateAll)
  * Stock import (ImportStockLog)
  * Pricelist creation (CreateWithProgress)
- Implemented unified polling for task status and DB connection in frontend
- Added task indicator in top bar showing running tasks count
- Added toast notifications for task completion/error
- Tasks automatically cleaned up after 10 minutes
- Tasks show progress (0-100%) with descriptive messages
- Updated handler constructors to receive task manager
- Added API endpoints for task status (/api/tasks, /api/tasks/:id)

Fixes issue with SSE disconnection on slow connections during long-running operations

cmd/pfs/main.go

@@ -30,6 +30,7 @@ import (
 	"git.mchus.pro/mchus/priceforge/internal/services/alerts"
 	"git.mchus.pro/mchus/priceforge/internal/services/pricelist"
 	"git.mchus.pro/mchus/priceforge/internal/services/pricing"
+	"git.mchus.pro/mchus/priceforge/internal/tasks"
 	"github.com/gin-gonic/gin"
 	mysqlDriver "github.com/go-sql-driver/mysql"
 	"gopkg.in/yaml.v3"
@@ -338,6 +339,9 @@ func setupRouter(cfg *config.Config, configPath string, connMgr *db.ConnectionMa
 	pricelistService := pricelist.NewService(mariaDB, pricelistRepo, componentRepo, pricingService)
 	stockImportService := services.NewStockImportService(mariaDB, pricelistService)
 
+	// Create task manager
+	taskManager := tasks.NewManager()
+
 	templatesPath := filepath.Join("web", "templates")
 	componentHandler := handlers.NewComponentHandler(componentService)
 	pricingHandler := handlers.NewPricingHandler(
@@ -345,12 +349,15 @@ func setupRouter(cfg *config.Config, configPath string, connMgr *db.ConnectionMa
 		pricingService,
 		alertService,
 		componentRepo,
+		componentService,
 		priceRepo,
 		statsRepo,
 		stockImportService,
 		dbUser,
+		taskManager,
 	)
-	pricelistHandler := handlers.NewPricelistHandler(pricelistService, dbUser)
+	pricelistHandler := handlers.NewPricelistHandler(pricelistService, dbUser, taskManager)
+	taskHandler := tasks.NewHandler(taskManager)
 	webHandler, err := handlers.NewWebHandler(templatesPath, componentService)
 	if err != nil {
 		return nil, err
@@ -550,6 +557,9 @@ func setupRouter(cfg *config.Config, configPath string, connMgr *db.ConnectionMa
 			c.JSON(http.StatusOK, gin.H{"message": "pong"})
 		})
 
+		api.GET("/tasks", taskHandler.List)
+		api.GET("/tasks/:id", taskHandler.Get)
+
 		components := api.Group("/components")
 		{
 			components.GET("", componentHandler.List)
@@ -583,6 +593,7 @@ func setupRouter(cfg *config.Config, configPath string, connMgr *db.ConnectionMa
 			pricingAdmin.GET("/lots", pricingHandler.ListLots)
 			pricingAdmin.GET("/lots-table", pricingHandler.ListLotsTable)
 			pricingAdmin.POST("/lots", pricingHandler.CreateLot)
+			pricingAdmin.POST("/lots/sync-metadata", pricingHandler.SyncLotsMetadata)
 			pricingAdmin.POST("/stock/import", pricingHandler.ImportStockLog)
 			pricingAdmin.GET("/stock/mappings", pricingHandler.ListStockMappings)
 			pricingAdmin.POST("/stock/mappings", pricingHandler.UpsertStockMapping)