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/paths.go

@@ -0,0 +1,79 @@
+package lifecycle
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+var (
+	AppName    = "ollama app"
+	CLIName    = "ollama"
+	AppDir     = "/opt/Ollama"
+	AppDataDir = "/opt/Ollama"
+	// TODO - should there be a distinct log dir?
+	UpdateStageDir = "/tmp"
+	AppLogFile     = "/tmp/ollama_app.log"
+	ServerLogFile  = "/tmp/ollama.log"
+	UpgradeLogFile = "/tmp/ollama_update.log"
+	Installer      = "OllamaSetup.exe"
+)
+
+func init() {
+	if runtime.GOOS == "windows" {
+		AppName += ".exe"
+		CLIName += ".exe"
+		// Logs, configs, downloads go to LOCALAPPDATA
+		localAppData := os.Getenv("LOCALAPPDATA")
+		AppDataDir = filepath.Join(localAppData, "Ollama")
+		UpdateStageDir = filepath.Join(AppDataDir, "updates")
+		AppLogFile = filepath.Join(AppDataDir, "app.log")
+		ServerLogFile = filepath.Join(AppDataDir, "server.log")
+		UpgradeLogFile = filepath.Join(AppDataDir, "upgrade.log")
+
+		// Executables are stored in APPDATA
+		AppDir = filepath.Join(localAppData, "Programs", "Ollama")
+
+		// Make sure we have PATH set correctly for any spawned children
+		paths := strings.Split(os.Getenv("PATH"), ";")
+		// Start with whatever we find in the PATH/LD_LIBRARY_PATH
+		found := false
+		for _, path := range paths {
+			d, err := filepath.Abs(path)
+			if err != nil {
+				continue
+			}
+			if strings.EqualFold(AppDir, d) {
+				found = true
+			}
+		}
+		if !found {
+			paths = append(paths, AppDir)
+
+			pathVal := strings.Join(paths, ";")
+			slog.Debug("setting PATH=" + pathVal)
+			err := os.Setenv("PATH", pathVal)
+			if err != nil {
+				slog.Error(fmt.Sprintf("failed to update PATH: %s", err))
+			}
+		}
+
+		// Make sure our logging dir exists
+		_, err := os.Stat(AppDataDir)
+		if errors.Is(err, os.ErrNotExist) {
+			if err := os.MkdirAll(AppDataDir, 0o755); err != nil {
+				slog.Error(fmt.Sprintf("create ollama dir %s: %v", AppDataDir, err))
+			}
+		}
+
+	} else if runtime.GOOS == "darwin" {
+		// TODO
+		AppName += ".app"
+		// } else if runtime.GOOS == "linux" {
+		// TODO
+	}
+}