[client] Create GUI windows on demand and destroy them on close (#7096)

The main and Settings windows were created at startup and kept alive hidden on close, so an idle tray held two webview processes for surfaces the user may never open. Both are now built on first show and destroyed on close, which takes the idle footprint on macOS from ~160 MB to ~74 MB.

The WindowManager owns creation: it rebuilds the main window on the next show and hands out live pointers, since a stored one goes stale. Every show is deferred until the frontend reports it has rendered, so a freshly created window is never on screen empty, with a timeout so a frontend that never reports cannot strand a window hidden.

client/ui/tray_update.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"context"
+	neturl "net/url"
 	"sync"
 	"time"
 
@@ -19,7 +20,7 @@ import (
 // trayUpdater owns the tray UI that reacts to auto-update. Composed inside Tray.
 type trayUpdater struct {
 	app          *application.App
-	window       *application.WebviewWindow
+	showMainAt   func(url string)
 	update       *services.Update
 	notifier     *Notifier
 	loc          *Localizer
@@ -36,10 +37,10 @@ type trayUpdater struct {
 	progressWindowOpen bool
 }
 
-func newTrayUpdater(app *application.App, window *application.WebviewWindow, update *services.Update, notifier *Notifier, loc *Localizer, onIconChange func(), onMenuChange func()) *trayUpdater {
+func newTrayUpdater(app *application.App, showMainAt func(url string), update *services.Update, notifier *Notifier, loc *Localizer, onIconChange func(), onMenuChange func()) *trayUpdater {
 	u := &trayUpdater{
 		app:          app,
-		window:       window,
+		showMainAt:   showMainAt,
 		update:       update,
 		notifier:     notifier,
 		loc:          loc,
@@ -185,14 +186,12 @@ func (u *trayUpdater) sendUpdateNotification(st updater.State) {
 // openProgressWindow points the main window at the /update progress page and
 // brings it forward.
 func (u *trayUpdater) openProgressWindow(version string) {
-	if u.window == nil {
+	if u.showMainAt == nil {
 		return
 	}
 	url := "/#/update"
 	if version != "" {
-		url += "?version=" + version
+		url += "?version=" + neturl.QueryEscape(version)
 	}
-	u.window.SetURL(url)
-	u.window.Show()
-	u.window.Focus()
+	u.showMainAt(url)
 }