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.

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Co-authored-by: mixeme <mix.public@ya.ru>
Reviewed-on: #1

scripts/build-windows.bat

@@ -6,7 +6,7 @@ REM directory. Move to the repository root (the parent of scripts\) before using
 REM relative paths such as .\cmd\gosentry and packaging\windows\gosentry.rc.
 cd /d "%~dp0\.."
 
-for /f "tokens=4" %%V in ('findstr /C:"var Version" src\core\version.go') do set "VERSION=%%~V"
+for /f "tokens=4" %%V in ('findstr /C:"var Version" src\app\version.go') do set "VERSION=%%~V"
 if "%VERSION%"=="" set "VERSION=0.0.0-dev"
 set "VERSION=%VERSION:"=%"
 
@@ -47,7 +47,7 @@ if %ERRORLEVEL%==0 (
 REM -trimpath removes local machine paths from the binary, -s -w reduce binary
 REM size, and -H=windowsgui prevents a separate console window from opening when
 REM the GUI app starts from Explorer or a shortcut.
-"%GOEXE%" build -trimpath -ldflags "-s -w -H=windowsgui -X gitea.mixdep.ru/mix/gosentry/src/core.Version=%VERSION%" -o "%OUTPUT%" .\cmd\gosentry
+"%GOEXE%" build -trimpath -ldflags "-s -w -H=windowsgui -X gitea.mixdep.ru/mix/gosentry/src/app.Version=%VERSION%" -o "%OUTPUT%" .\cmd\gosentry
 if errorlevel 1 exit /b 1
 
 REM Icons are embedded into the executable, so no assets directory is copied next