refactor(background): parameterize sync queue and worker pool constructors

Split each constructor into a default-args wrapper and a config-accepting
variant so the sync queue interval/batch size and the worker pool size/
queue cap can be sourced from the settings registry at startup. These
values are constructed once at boot, so they are tagged requires_restart
in the admin UI.

queue.go:
- NewSyncQueueProcessorWithConfig(db, interval, batchSize) takes the
  flush interval and batch size as parameters; NewSyncQueueProcessor
  becomes a thin wrapper with the historical 5s / 50 defaults.

worker.go:
- NewWorkerWithConfig(numWorkers, queueCap, connManager) takes the
  queue capacity as a parameter; NewWorker becomes a thin wrapper with
  the historical cap of 100.

No behavior change for existing callers; main.go will switch to the
config-accepting variants in a follow-up wiring commit.

internal/services/worker.go

@@ -176,10 +176,17 @@ func (w *Worker) GetActiveJobCount() int {
 	return count
 }
 func NewWorker(numWorkers int, connManager *wsync.ConnectionManager) *Worker {
+	return NewWorkerWithConfig(numWorkers, 100, connManager)
+}
+
+// NewWorkerWithConfig constructs a worker pool with the given worker count and
+// job-queue capacity. Used at startup to source values from the settings
+// registry.
+func NewWorkerWithConfig(numWorkers, queueCap int, connManager *wsync.ConnectionManager) *Worker {
 	ctx, cancel := context.WithCancel(context.Background())
 
 	w := &Worker{
-		jobQueue: make(chan *Job, 100),
+		jobQueue: make(chan *Job, queueCap),
 		results:  make(map[string]*JobResult),
 		ctx:      ctx,
 		cancel:   cancel,
@@ -995,3 +1002,4 @@ func (w *Worker) Shutdown() {
 	close(w.jobQueue)
 	w.wg.Wait()
 }
+