feat(notifications): add opt-in timeout progress bar on popups (#2587)

Adds a thin bar pinned to the bottom of the notification card that drains
full->empty over the auto-dismiss timer, as a visual countdown to
dismissal. Opt-in via notificationShowTimeoutBar (default off), with a
toggle in Settings > Notifications. Shown for any timed notification
(timer.interval > 0, including timed criticals); inset by the corner
radius, and frozen while hovered or during the exit animation. Plain
Rectangle - no offscreen textures or shader passes. A Connections on the
timer resets the bar on every (re)start, including the in-place restart
on a deduped notification.

Co-authored-by: bogdan-velicu <hydrotech074@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

quickshell/Modules/Settings/NotificationsTab.qml

@@ -273,6 +273,15 @@ Item {
                     onToggled: checked => SettingsData.set("notificationCompactMode", checked)
                 }
 
+                SettingsToggleRow {
+                    settingKey: "notificationShowTimeoutBar"
+                    tags: ["notification", "timeout", "progress", "bar", "timer", "countdown"]
+                    text: I18n.tr("Timeout Progress Bar")
+                    description: I18n.tr("Show a bar that drains as the popup's auto-dismiss timer runs")
+                    checked: SettingsData.notificationShowTimeoutBar
+                    onToggled: checked => SettingsData.set("notificationShowTimeoutBar", checked)
+                }
+
                 SettingsToggleRow {
                     settingKey: "notificationDedupeEnabled"
                     tags: ["notification", "duplicate", "dedupe", "stack", "coalesce", "repeat"]