feat(notify): Windows toasts under talk's own identity, icon on Linux

The daemon (and talk test --toast) now register the AppUserModelID
m3ta.talk under HKCU with display name and the installed icon, so
toasts appear as "talk" with the icon instead of Windows PowerShell;
the PowerShell identity stays as fallback until the registration has
run once. The redundant "talk" title line is dropped under the own
identity. notify.Setup bundles icon install, identity and the talk:
protocol handler for both callers. Linux notifications carry the
installed icon as app_icon. doctor names the active identity.

Verified on the Windows 11 VM: registry key, icon file, toast with
working Cancel button, exe icon; Linux via quickshell.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/daemon/daemon.go

@@ -15,7 +15,6 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -85,13 +84,12 @@ func Run(ctx context.Context, opts Options) error {
 	if err != nil {
 		return err
 	}
-	// Windows: the toast's Cancel button opens a talk: link; register the
-	// protocol handler for this user so the click starts `talk uri`.
-	if cfg.Notify.OnSpeak && runtime.GOOS == "windows" {
-		if exe, err := os.Executable(); err == nil {
-			if err := notify.RegisterProtocol(exe); err != nil {
-				logger.Printf("warning: %v; the toast's Cancel button will not work", err)
-			}
+	// Desktop side: the icon next to the config, Windows additionally the
+	// toast identity and the talk: protocol handler for the Cancel button.
+	if dir, err := config.Dir(getenv); err == nil {
+		exe, _ := os.Executable()
+		if err := notify.Setup(dir, exe); err != nil {
+			logger.Printf("warning: %v; notifications fall back to the plain identity or lose the Cancel button", err)
 		}
 	}