Implement new Go based Desktop app

This focuses on Windows first, but coudl be used for Mac
and possibly linux in the future.

app/lifecycle/updater_windows.go

@@ -0,0 +1,79 @@
+package lifecycle
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+func DoUpgrade(cancel context.CancelFunc, done chan int) error {
+	files, err := filepath.Glob(filepath.Join(UpdateStageDir, "*", "*.exe")) // TODO generalize for multiplatform
+	if err != nil {
+		return fmt.Errorf("failed to lookup downloads: %s", err)
+	}
+	if len(files) == 0 {
+		return fmt.Errorf("no update downloads found")
+	} else if len(files) > 1 {
+		// Shouldn't happen
+		slog.Warn(fmt.Sprintf("multiple downloads found, using first one %v", files))
+	}
+	installerExe := files[0]
+
+	slog.Info("starting upgrade with " + installerExe)
+	slog.Info("upgrade log file " + UpgradeLogFile)
+
+	// When running in debug mode, we'll be "verbose" and let the installer pop up and prompt
+	installArgs := []string{
+		"/CLOSEAPPLICATIONS",                    // Quit the tray app if it's still running
+		"/LOG=" + filepath.Base(UpgradeLogFile), // Only relative seems reliable, so set pwd
+		"/FORCECLOSEAPPLICATIONS",               // Force close the tray app - might be needed
+	}
+	// When we're not in debug mode, make the upgrade as quiet as possible (no GUI, no prompts)
+	// TODO - temporarily disable since we're pinning in debug mode for the preview
+	// if debug := os.Getenv("OLLAMA_DEBUG"); debug == "" {
+	installArgs = append(installArgs,
+		"/SP", // Skip the "This will install... Do you wish to continue" prompt
+		"/SUPPRESSMSGBOXES",
+		"/SILENT",
+		"/VERYSILENT",
+	)
+	// }
+
+	// Safeguard in case we have requests in flight that need to drain...
+	slog.Info("Waiting for server to shutdown")
+	cancel()
+	if done != nil {
+		<-done
+	} else {
+		slog.Warn("XXX done chan was nil, not actually waiting")
+	}
+
+	slog.Debug(fmt.Sprintf("starting installer: %s %v", installerExe, installArgs))
+	os.Chdir(filepath.Dir(UpgradeLogFile)) //nolint:errcheck
+	cmd := exec.Command(installerExe, installArgs...)
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("unable to start ollama app %w", err)
+	}
+
+	if cmd.Process != nil {
+		err = cmd.Process.Release()
+		if err != nil {
+			slog.Error(fmt.Sprintf("failed to release server process: %s", err))
+		}
+	} else {
+		// TODO - some details about why it didn't start, or is this a pedantic error case?
+		return fmt.Errorf("installer process did not start")
+	}
+
+	// TODO should we linger for a moment and check to make sure it's actually running by checking the pid?
+
+	slog.Info("Installer started in background, exiting")
+
+	os.Exit(0)
+	// Not reached
+	return nil
+}