T5.2: Introduce autostart.Manager interface + per-platform impls

Define Manager with Set/Status in autostart.go; add concrete types
(windowsManager, linuxManager, otherManager) in the per-platform files.
Service gains a manager field wired by Open() via autostart.New();
AutostartStatus and ApplyAutostart delegate to it instead of calling
package-level functions directly. Tests that don't need autostart get a
nil manager, which is safe (no-op returns).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/service.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"gitea.mixdep.ru/mix/gosentry/src/domain"
+	"gitea.mixdep.ru/mix/gosentry/src/platform/autostart"
 	"gitea.mixdep.ru/mix/gosentry/src/runner"
 	"gitea.mixdep.ru/mix/gosentry/src/scheduler"
 	"gitea.mixdep.ru/mix/gosentry/src/storage"
@@ -58,6 +59,10 @@ type Service struct {
 	sched  *scheduler.Scheduler
 	cancel context.CancelFunc
 
+	// manager is the platform autostart implementation. It is nil in tests that
+	// do not exercise autostart; Open() wires it via autostart.New().
+	manager autostart.Manager
+
 	// observers and their guard live in events.go. dispatchMu is separate from mu
 	// so that emitting an event never requires (or is held under) the state lock:
 	// the Service must release mu before dispatching, per the locking contract.
@@ -136,7 +141,9 @@ func Open() (*Service, error) {
 	if err != nil {
 		return nil, err
 	}
-	return NewService(store, jobs), nil
+	svc := NewService(store, jobs)
+	svc.manager = autostart.New()
+	return svc, nil
 }
 
 // Store returns the underlying store. It is exposed so callers that still need