fix(ui): portal tooltips, opaque glass, settings rail+stable height, notif test, channel help

- Tooltip: render in a portal with fixed positioning + edge-flip so hints are never
  clipped by overflow/stacking ancestors (fixes mispositioned/hidden bubbles app-wide).
- Glass: raise opacity so overlay menus/panels stay readable over content.
- SettingsPanel: vertical tab rail (no wrapping/jumping), content grid-stacked so the
  panel sizes to the tallest tab (stable height) and floats to its content height.
- Notifications: the test toast is now a normal auto-dismissing toast (with countdown
  bar) that also plays the sound via a new force-sound flag.
- Channel manager: explain priority/tags/hide and what 'Sync subscriptions' does;
  add a 'Channel priority' feed sort so priority is actually meaningful.

frontend/src/lib/notifications.ts

@@ -41,6 +41,7 @@ export interface NotifyInput {
   action?: NotifAction;
   meta?: NotifMeta;
   requiresInteraction?: boolean;
+  sound?: boolean; // force the alert tone (when sound is enabled) even for an info toast
 }
 
 const HISTORY_KEY = "subfeed.notifications";
@@ -177,7 +178,7 @@ export function notify(input: NotifyInput): number {
     },
   ];
   emit();
-  if (config.sound && (requiresInteraction || level === "error" || level === "fatal")) {
+  if (config.sound && (input.sound || requiresInteraction || level === "error" || level === "fatal")) {
     beep();
   }
   if (duration) setTimeout(() => dismiss(id), duration);