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/mainwindow.go

@@ -0,0 +1,92 @@
+package ui
+
+import (
+	"time"
+
+	"gitea.mixdep.ru/mix/gosentry/assets"
+	"gitea.mixdep.ru/mix/gosentry/src/app"
+	"gitea.mixdep.ru/mix/gosentry/src/domain"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/container"
+	"fyne.io/fyne/v2/theme"
+	"fyne.io/fyne/v2/widget"
+)
+
+// The UI package aliases domain types to keep widget callbacks short. The actual
+// durable model still lives in src/domain, so UI code does not define a second
+// copy of the scheduler data.
+type job = domain.Job
+type event = domain.RunRecord
+
+func newMainView(w fyne.Window) (fyne.CanvasObject, func(time.Duration, bool)) {
+	svc, err := app.Open()
+	if err != nil {
+		return container.NewPadded(widget.NewLabel("Failed to load GoSentry configuration: " + err.Error())), func(time.Duration, bool) {}
+	}
+	svc.InstallDesktopIcon(appID, assets.IconBytes())
+
+	// Build the initial event history from the current runtime state. Jobs and
+	// runtimes are read here only for this one-time initialization; the jobs view
+	// owns all subsequent state via its own syncFromService closure.
+	initialJobs := svc.Jobs()
+	initialRuntimes := make(map[int]*domain.JobRuntime, len(initialJobs))
+	for _, j := range initialJobs {
+		if rt := svc.Runtime(j.ID); rt != nil {
+			initialRuntimes[j.ID] = rt
+		}
+	}
+	events := collectActivity(initialJobs, initialRuntimes)
+
+	jobsPanel, refreshJobsView := newJobsView(w, svc)
+
+	history := newHistoryView(&events)
+	recordStartup := func(duration time.Duration, windowShown bool) {
+		// Startup is recorded as an in-memory History event instead of being
+		// persisted into jobs.yaml. It is session diagnostics, not durable job
+		// state, and keeping it ephemeral avoids polluting the human-editable YAML
+		// file with process-lifetime bookkeeping.
+		detail := "Window shown in " + duration.Round(time.Millisecond).String()
+		if !windowShown {
+			detail = "Started in tray in " + duration.Round(time.Millisecond).String()
+		}
+		events = append(events, newEvent(0, "Application", "Started", detail))
+		history.Refresh()
+	}
+
+	refresh := func() {
+		refreshJobsView()
+		history.Refresh()
+	}
+
+	// The Service announces every change through events. This single listener is
+	// where the UI reacts: it appends run/activity records to History and redraws.
+	// Events fire from two contexts — UI button handlers call into the Service
+	// synchronously (main goroutine), while scheduled and manual run completions
+	// emit from the run goroutine. fyne.Do marshals all of this widget work onto
+	// the main thread in both cases, so the engine never mutates Fyne state off
+	// the UI thread. This is the sole place events touch widgets. (Resolves #4.)
+	svc.Subscribe(app.ObserverFunc(func(ev app.Event) {
+		recorded, isRecorded := ev.(app.RunRecorded)
+		errOccurred, isError := ev.(app.ErrorOccurred)
+		fyne.Do(func() {
+			if isRecorded {
+				events = append(events, recorded.Record)
+			}
+			if isError {
+				events = append(events, newEvent(0, "Service", "Error", errOccurred.Err.Error()))
+			}
+			refresh()
+		})
+	}))
+	svc.Start()
+
+	tabs := container.NewAppTabs(
+		container.NewTabItemWithIcon("Jobs", theme.ListIcon(), jobsPanel),
+		container.NewTabItemWithIcon("History", theme.HistoryIcon(), history),
+		container.NewTabItemWithIcon("Settings", theme.SettingsIcon(), settingsView(w, svc)),
+	)
+	tabs.SetTabLocation(container.TabLocationTop)
+
+	return tabs, recordStartup
+}