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

scripts/test.bat

@@ -0,0 +1,35 @@
+@echo off
+setlocal enabledelayedexpansion
+REM GoSentry test runner
+REM Runs go vet and go test with race detection
+
+REM Move to repository root
+cd /d "%~dp0\.."
+
+REM Fyne uses native libraries through CGO. MSYS2 UCRT64 provides the GCC toolchain
+REM expected by the Windows build; prepending it keeps the script self-contained
+REM without permanently changing the user's system PATH.
+if exist "C:\msys64\ucrt64\bin" set "PATH=C:\msys64\ucrt64\bin;%PATH%"
+
+REM Race detector requires CGO
+set "CGO_ENABLED=1"
+
+echo Running go vet...
+go vet ./...
+if errorlevel 1 (
+    echo.
+    echo ✗ go vet failed
+    exit /b 1
+)
+
+echo.
+echo Running go test with race detection...
+go test -race ./...
+if errorlevel 1 (
+    echo.
+    echo ✗ go test failed
+    exit /b 1
+)
+
+echo.
+echo ✓ All tests passed