feat(notify): desktop notification per announcement with a Cancel button

Every playing announcement now shows a desktop notification with its text
and, on Linux, a Cancel button (Abbrechen for German) that stops exactly
that announcement; the notification is closed when the announcement ends.
This brings back what the old talk.sh had with notify-send --action, as a
default: a long announcement can be cut short without a terminal.

Implementation: the freedesktop Notifications service on the session bus
via godbus (pure Go): one connection per process, Notify with the action
list, ActionInvoked dispatched to the announcement, CloseNotification at
the end, expire_timeout 0 so the button stays for the whole announcement.
Without a session bus the notify-send fallback shows a plain notification;
macOS and Windows show one without a button for now. queue.CancelItem(id)
cancels only the playing item. Config [notify] on_speak (default true, env
TALK_NOTIFY). `talk test --toast` now shows the real thing and waits for a
click; `talk doctor` names the service and whether it supports the button.

Config hygiene found on the way: a key written below a [table] header
belongs to that table in TOML (lang under [voice] was silently ignored).
config.Load now collects unknown keys (undecoded ones and non-language
keys under [voice.<provider>]) and `talk doctor` warns with the hint.

Tests: process test on a private dbus-daemon with a fake
org.freedesktop.Notifications service (Notify payload, cancel click aborts
the synthesis, CloseNotification), queue.CancelItem, config keys. All test
binaries point DBUS_SESSION_BUS_ADDRESS at a dead socket so no test ever
pops a notification on the developer's desktop. flake vendorHash updated
for the new dependency.

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

internal/daemon/daemon.go

@@ -84,7 +84,34 @@ func Run(ctx context.Context, opts Options) error {
 	if err != nil {
 		return err
 	}
-	q := queue.New(queue.Laws{
+	// Desktop notification per announcement (notify.on_speak): shown when the
+	// announcement starts, with a Cancel button where the platform has one,
+	// closed when it ends. Best effort: the first failure is logged, later
+	// ones are silent, speech never waits for a notification problem.
+	var q *queue.Queue
+	var notifyFailed sync.Once
+	announceNotification := func(ctx context.Context, item queue.Item, lang string) func() {
+		if !cfg.Notify.OnSpeak {
+			return func() {}
+		}
+		label := "Cancel"
+		if lang == "de" {
+			label = "Abbrechen"
+		}
+		closeFn, err := notify.Announce(ctx, item.Text, label, func() {
+			if q.CancelItem(item.ID) {
+				logger.Printf("announcement %s cancelled from its notification", item.ID)
+			}
+		})
+		if err != nil {
+			notifyFailed.Do(func() {
+				logger.Printf("warning: notifications unavailable (%v); announcements play without one. Set [notify] on_speak = false to silence this", err)
+			})
+		}
+		return closeFn
+	}
+
+	q = queue.New(queue.Laws{
 		RateLimit:      cfg.Queue.RateLimit,
 		AllowHighBurst: cfg.Queue.AllowHighBurst,
 		Quiet:          quiet,
@@ -92,12 +119,10 @@ func Run(ctx context.Context, opts Options) error {
 		MaxText:        cfg.Queue.MaxText,
 		MaxAge:         cfg.Queue.MaxAge,
 	}, func(ctx context.Context, item queue.Item) error {
-		out, err := engine.Speak(ctx, speak.Request{
-			Text:     item.Text,
-			Lang:     item.Lang,
-			Provider: item.Provider,
-			Voice:    item.Voice,
-		})
+		req := speak.Request{Text: item.Text, Lang: item.Lang, Provider: item.Provider, Voice: item.Voice}
+		closeNotification := announceNotification(ctx, item, engine.Lang(req))
+		defer closeNotification()
+		out, err := engine.Speak(ctx, req)
 		if err == nil && !out.Discarded {
 			logger.Printf("announcement %s via %s (synthesis %s, playback %s)", item.ID, out.Provider,
 				out.Synthesis.Round(time.Millisecond), out.Playback.Round(time.Millisecond))
@@ -175,8 +200,8 @@ func Run(ctx context.Context, opts Options) error {
 	if len(cfg.Server.AllowedOrigins) > 0 {
 		corsLog = fmt.Sprintf("%v", cfg.Server.AllowedOrigins)
 	}
-	logger.Printf("listening on http://%s (version %s, pid %d, audio sink %s, mute=%v, rate-limit %s, high-burst=%v, max-text %d, max-age %s, quiet-hours=%q mode %s, cors=%s, mcp=/mcp)",
-		addr, opts.Version, os.Getpid(), engine.SinkName(), mute.Muted(),
+	logger.Printf("listening on http://%s (version %s, pid %d, audio sink %s, mute=%v, notify=%v, rate-limit %s, high-burst=%v, max-text %d, max-age %s, quiet-hours=%q mode %s, cors=%s, mcp=/mcp)",
+		addr, opts.Version, os.Getpid(), engine.SinkName(), mute.Muted(), cfg.Notify.OnSpeak,
 		cfg.Queue.RateLimit, cfg.Queue.AllowHighBurst, cfg.Queue.MaxText, cfg.Queue.MaxAge, cfg.QuietHours, cfg.QuietMode, corsLog)
 
 	select {