feat: add user-scoped WebSocket broadcasting for scan progress

- Add UserID field to Job struct for tracking job ownership
- Broadcast scan progress updates to user's WebSocket connections
- Send real-time updates during scanning (progress, files scanned, new items, errors)

This allows the frontend to display live scan progress without HTTP polling.
Scanner now associates scan jobs with requesting user for targeted updates.

internal/handlers/scanner.go

@@ -86,8 +86,9 @@ func (h *Handler) ScanLibrary(c echo.Context) error {
 	jobID := uuid.New().String()
 
 	job := &services.Job{
-		ID:   jobID,
-		Type: services.JobTypeScan,
+		ID:     jobID,
+		Type:   services.JobTypeScan,
+		UserID: userID,
 		Params: map[string]interface{}{
 			"library_id": req.LibraryID,
 			"folders":    folderPaths,

internal/services/worker.go

@@ -2,6 +2,7 @@ package services
 
 import (
 	"bookhoard/internal/database"
+	wsync "bookhoard/internal/sync"
 	"context"
 	"fmt"
 	"net/http"
@@ -53,6 +54,7 @@ func (w *Worker) Enqueue(job *Job) {
 type Job struct {
 	ID               string
 	Type             JobType
+	UserID           string
 	Params           map[string]interface{}
 	Status           JobStatus
 	CreatedAt        time.Time
@@ -84,6 +86,7 @@ type JobResult struct {
 type Worker struct {
 	jobQueue     chan *Job
 	results      map[string]*JobResult
+	connManager  *wsync.ConnectionManager
 	mu           sync.RWMutex
 	wg           sync.WaitGroup
 	ctx          context.Context
@@ -91,7 +94,7 @@ type Worker struct {
 	shuttingDown atomic.Bool
 }
 
-func NewWorker(numWorkers int) *Worker {
+func NewWorker(numWorkers int, connManager *wsync.ConnectionManager) *Worker {
 	ctx, cancel := context.WithCancel(context.Background())
 
 	w := &Worker{
@@ -106,6 +109,8 @@ func NewWorker(numWorkers int) *Worker {
 		go w.worker()
 	}
 
+	w.connManager = connManager
+
 	return w
 }
 
@@ -249,6 +254,21 @@ func (w *Worker) processScanJob(job *Job) (interface{}, error) {
 			result.NewItems = newItems
 			result.Errors = errors
 		}
+		// Broadcast via WebSocket to user
+		if w.connManager != nil && job.UserID != "" {
+			msg := wsync.BroadcastMessage{
+				Type: wsync.MessageTypeScanProgress,
+				Data: map[string]interface{}{
+					"job_id":        job.ID,
+					"progress":      progress,
+					"files_scanned": filesScanned,
+					"new_items":     newItems,
+					"errors":        errors,
+				},
+			}
+
+			w.connManager.BroadcastToUser(job.UserID, msg)
+		}
 	}
 
 	if err := scanner.SetFolders(folders); err != nil {