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/runner/logfile.go

@@ -0,0 +1,55 @@
+package runner
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+	"unicode"
+
+	"gitea.mixdep.ru/mix/gosentry/src/domain"
+)
+
+func writeRunLog(logsDir string, job domain.Job, trigger string, state string, detail string, output string, started time.Time) string {
+	if strings.TrimSpace(logsDir) == "" {
+		return ""
+	}
+	if err := os.MkdirAll(logsDir, 0o755); err != nil {
+		return ""
+	}
+	// The timestamp comes first so a plain directory listing is naturally sorted
+	// by run time. The job name is included for human scanning, but sanitized to
+	// avoid characters that are invalid on Windows or awkward on shells.
+	fileName := started.Format("20060102-150405") + "_" + sanitizeFileName(job.Name) + ".log"
+	path := filepath.Join(logsDir, fileName)
+	content := fmt.Sprintf("time: %s\njob_id: %d\njob_name: %s\ntrigger: %s\nstate: %s\ndetail: %s\ncommand: %s\narguments: %s\nsuccess_exit_codes: %s\nstart_only: %t\n\n%s\n",
+		started.Format("2006-01-02 15:04:05"), job.ID, job.Name, trigger, state, detail, job.Command, logArguments(job.Arguments), successExitCodesText(job), job.StartOnly, output)
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		return ""
+	}
+	return path
+}
+
+func sanitizeFileName(name string) string {
+	name = strings.TrimSpace(name)
+	if name == "" {
+		return "job"
+	}
+	var builder strings.Builder
+	for _, r := range name {
+		switch {
+		case unicode.IsLetter(r), unicode.IsDigit(r):
+			builder.WriteRune(r)
+		case r == '-', r == '_':
+			builder.WriteRune(r)
+		default:
+			builder.WriteRune('_')
+		}
+	}
+	result := strings.Trim(builder.String(), "_")
+	if result == "" {
+		return "job"
+	}
+	return result
+}