Refactoring complete: v0.4.0 architectural milestone (#1)

## Summary

Completed Phase 5 refactoring and reached the target architecture.

**Architectural milestone achieved:**
- Service layer owns all state and is the sole writer
- UI is a thin Fyne view, all widget updates marshaled via `fyne.Do`
- Core engines are stateless and injectable
- Domain types are pure (no `yaml:"-"` fields)
- Full module builds and `go vet ./...` clean

## Changes

- Bump version: 0.3.6 → 0.4.0
- Update CHANGELOG with Phase 5 summary
- Add ROADMAP "Refactoring Follow-Ups" section

## Known follow-up work

1. **Linux test build broken** — `runner_test.go` needs `//go:build windows` tag
2. **File-size limits exceeded** — `operations.go` (486 lines), `jobs_view.go` (415 lines)

See ROADMAP.md for details.

---------

Co-authored-by: mixeme <mix.public@ya.ru>
Reviewed-on: #1

src/app/platform.go

@@ -0,0 +1,43 @@
+package app
+
+import (
+	"gitea.mixdep.ru/mix/gosentry/src/platform/desktop"
+)
+
+// InstallDesktopIcon installs the application's .desktop file and icon on
+// Linux (no-op on other platforms). The resulting icon path is stored in
+// store.Paths.DesktopIcon so ApplyAutostart can reference it.
+func (s *Service) InstallDesktopIcon(appID string, iconBytes []byte) {
+	if iconPath, err := desktop.InstallDesktopIntegration(appID, s.store.Paths.ExecutablePath, iconBytes); err == nil {
+		s.store.Paths.DesktopIcon = iconPath
+	}
+}
+
+// AutostartStatus reports whether the platform autostart entry matches the
+// current StartOnLogin setting in the stored config.
+func (s *Service) AutostartStatus() (ok bool, message string) {
+	s.mu.Lock()
+	enabled := s.store.Config.StartOnLogin
+	execPath := s.store.Paths.ExecutablePath
+	manager := s.manager
+	s.mu.Unlock()
+	if manager == nil {
+		return false, "autostart not available"
+	}
+	return manager.Status(enabled, execPath)
+}
+
+// ApplyAutostart writes or removes the platform autostart entry to match the
+// current StartOnLogin setting in the stored config. Call after UpdateSettings.
+func (s *Service) ApplyAutostart() error {
+	s.mu.Lock()
+	enabled := s.store.Config.StartOnLogin
+	execPath := s.store.Paths.ExecutablePath
+	iconPath := s.store.Paths.DesktopIcon
+	manager := s.manager
+	s.mu.Unlock()
+	if manager == nil {
+		return nil
+	}
+	return manager.Set(enabled, execPath, iconPath)
+}