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/platform/autostart/autostart_other.go

@@ -0,0 +1,32 @@
+//go:build !windows && !linux
+
+package autostart
+
+import "fmt"
+
+type otherManager struct{}
+
+// New returns the stub autostart Manager for unsupported platforms.
+func New() Manager { return otherManager{} }
+
+func (otherManager) Set(enabled bool, executablePath, iconPath string) error {
+	return SetAutostart(enabled, executablePath, iconPath)
+}
+
+func (otherManager) Status(expectedEnabled bool, executablePath string) (bool, string) {
+	return AutostartStatus(expectedEnabled, executablePath)
+}
+
+func SetAutostart(enabled bool, executablePath string, iconPath string) error {
+	if !enabled {
+		return nil
+	}
+	return fmt.Errorf("autostart is not implemented for this platform")
+}
+
+func AutostartStatus(expectedEnabled bool, executablePath string) (bool, string) {
+	if !expectedEnabled {
+		return true, "Autostart is off"
+	}
+	return false, "Autostart is not implemented for this platform"
+}