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/domain/record.go

@@ -0,0 +1,15 @@
+package domain
+
+// RunRecord represents one visible activity item. Scheduled and manual command
+// output is also written to a log file; the in-memory Output copy exists so the
+// latest run can be displayed without reopening the log on every repaint.
+type RunRecord struct {
+	Time    string `yaml:"time"`
+	JobID   int    `yaml:"job_id"`
+	JobName string `yaml:"job_name"`
+	Trigger string `yaml:"trigger,omitempty"`
+	State   string `yaml:"state"`
+	Detail  string `yaml:"detail"`
+	LogFile string `yaml:"log_file,omitempty"`
+	Output  string `yaml:"output,omitempty"`
+}