Add manual update check to tray menu, /update/check endpoint

- Tray 'Check for Updates' now checks immediately and shows dialog
- Dialog has 'Install' and 'Later' buttons
- /update/check endpoint on local server for SPA to query

cmd/desktop/main.go

@@ -267,6 +267,31 @@ h1{font-size:18px;margin-bottom:8px}.ok{color:#22c55e;font-size:14px}</style>
 		json.NewEncoder(w).Encode(cfg)
 	})
 
+	mux.HandleFunc("/update/check", func(w http.ResponseWriter, r *http.Request) {
+		latest := fetchLatestRelease()
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		if latest == nil {
+			json.NewEncoder(w).Encode(map[string]string{"current": version})
+			return
+		}
+		hasAsset := false
+		for _, a := range latest.Assets {
+			if strings.Contains(a.Name, "darwin") {
+				hasAsset = true
+				updater.mu.Lock()
+				updater.latestURL = a.BrowserDownloadURL
+				updater.mu.Unlock()
+				break
+			}
+		}
+		json.NewEncoder(w).Encode(map[string]string{
+			"current":   version,
+			"latest":    latest.Version,
+			"has_asset": fmt.Sprintf("%t", hasAsset),
+		})
+	})
+
 	listener, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", oidcCallbackPort))
 	if err != nil {
 		log.Printf("OIDC server: %v", err)
@@ -683,7 +708,30 @@ func main() {
 	})
 	trayMenu.AddSeparator()
 	trayMenu.Add("Check for Updates").OnClick(func(ctx *application.Context) {
-		go checkUpdates()
+		go func() {
+			latest := fetchLatestRelease()
+			if latest == nil {
+				app.Dialog.Info().SetTitle("Up to Date").SetMessage("You are running the latest version (" + version + ").").Show()
+				return
+			}
+			for _, a := range latest.Assets {
+				if strings.Contains(a.Name, "darwin") {
+					updater.mu.Lock()
+					updater.latestURL = a.BrowserDownloadURL
+					updater.mu.Unlock()
+					msg := fmt.Sprintf("Version %s is available (you have %s). Install now?", latest.Version, version)
+					d := app.Dialog.Question().SetTitle("Update Available").SetMessage(msg)
+					yes := d.AddButton("Install")
+					yes.OnClick(func() { doUpdate(updater.latestURL) })
+					no := d.AddButton("Later")
+					d.SetDefaultButton(yes)
+					d.SetCancelButton(no)
+					d.Show()
+					return
+				}
+			}
+			app.Dialog.Info().SetTitle("Up to Date").SetMessage("You are running the latest version (" + version + ").").Show()
+		}()
 	})
 	trayMenu.AddSeparator()
 	trayMenu.Add("Quit").OnClick(func(ctx *application.Context) {