T1.7: Create src/platform/desktop; move desktop integration

Move desktop_linux.go and desktop_other.go from src/core to the new
src/platform/desktop package. Update src/gui to import and use the
new package location.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/gui/app.go

@@ -16,6 +16,7 @@ import (
 	"gitea.mixdep.ru/mix/gosentry/src/core"
 	"gitea.mixdep.ru/mix/gosentry/src/domain"
 	"gitea.mixdep.ru/mix/gosentry/src/platform/autostart"
+	"gitea.mixdep.ru/mix/gosentry/src/platform/desktop"
 	"gitea.mixdep.ru/mix/gosentry/src/runner"
 	"gitea.mixdep.ru/mix/gosentry/src/scheduler"
 	"gitea.mixdep.ru/mix/gosentry/src/storage"
@@ -168,7 +169,7 @@ func newMainView(w fyne.Window) (fyne.CanvasObject, func(time.Duration, bool)) {
 	if err != nil {
 		return container.NewPadded(widget.NewLabel("Failed to load GoSentry configuration: " + err.Error())), func(time.Duration, bool) {}
 	}
-	if iconPath, err := core.InstallDesktopIntegration(appID, store.Paths.ExecutablePath, assets.IconBytes()); err == nil {
+	if iconPath, err := desktop.InstallDesktopIntegration(appID, store.Paths.ExecutablePath, assets.IconBytes()); err == nil {
 		store.Paths.DesktopIcon = iconPath
 	}
 	events := collectActivity(jobs)

src/platform/desktop/desktop_linux.go

@@ -1,6 +1,6 @@
 //go:build linux
 
-package core
+package desktop
 
 import (
 	"fmt"

src/platform/desktop/desktop_other.go

@@ -1,6 +1,6 @@
 //go:build !linux
 
-package core
+package desktop
 
 func InstallDesktopIntegration(appID string, executablePath string, icon []byte) (string, error) {
 	return "", nil