fix: catalogue job always shows 0 counters after cancel/finish

Two bugs fixed in runScrapeTask / runCatalogueTask:

1. FinishScrapeTask was called with the task's own context, which is
   already cancelled when the task is stopped. The PATCH to PocketBase
   failed silently, leaving all counters at their initial zero values.
   Fix: use a fresh context.WithTimeout(Background, 15s) for the write.

2. BooksFound was double-counted: RunBook already sets BooksFound=1 on
   success, but the accumulation loop added an extra +1 unconditionally,
   reporting 2 books per successful scrape.
   Fix: result.BooksFound += bookResult.BooksFound  (drop the + 1).

backend/internal/runner/runner.go

@@ -505,7 +505,11 @@ func (r *Runner) runScrapeTask(ctx context.Context, task domain.ScrapeTask) {
 		log.Warn("runner: unknown task kind")
 	}
 
-	if err := r.deps.Consumer.FinishScrapeTask(ctx, task.ID, result); err != nil {
+	// Use a fresh context for the final write so a cancelled task context doesn't
+	// prevent the result counters from being persisted to PocketBase.
+	finishCtx, finishCancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer finishCancel()
+	if err := r.deps.Consumer.FinishScrapeTask(finishCtx, task.ID, result); err != nil {
 		log.Error("runner: FinishScrapeTask failed", "err", err)
 	}
 
@@ -551,7 +555,7 @@ func (r *Runner) runCatalogueTask(ctx context.Context, task domain.ScrapeTask, o
 			TargetURL: entry.URL,
 		}
 		bookResult := o.RunBook(ctx, bookTask)
-		result.BooksFound += bookResult.BooksFound + 1
+		result.BooksFound += bookResult.BooksFound
 		result.ChaptersScraped += bookResult.ChaptersScraped
 		result.ChaptersSkipped += bookResult.ChaptersSkipped
 		result.Errors += bookResult.Errors