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/ui/layout.go

@@ -0,0 +1,37 @@
+package ui
+
+import (
+	"fyne.io/fyne/v2"
+)
+
+type minWidthLayout struct {
+	width float32
+}
+
+func (l minWidthLayout) MinSize(objects []fyne.CanvasObject) fyne.Size {
+	width := l.width
+	var height float32
+	for _, object := range objects {
+		if !object.Visible() {
+			continue
+		}
+		min := object.MinSize()
+		if min.Width > width {
+			width = min.Width
+		}
+		if min.Height > height {
+			height = min.Height
+		}
+	}
+	return fyne.NewSize(width, height)
+}
+
+func (l minWidthLayout) Layout(objects []fyne.CanvasObject, size fyne.Size) {
+	for _, object := range objects {
+		if !object.Visible() {
+			continue
+		}
+		object.Move(fyne.NewPos(0, 0))
+		object.Resize(size)
+	}
+}