fix(toast): sticky toasts + improve update notification visibility (P5-40)

Add sticky?: boolean to ToastNotif — sticky toasts skip the 4s auto-dismiss
timer entirely, staying until the user clicks or manually dismisses. Sticky
toasts also use cyan accent/glow (vs orange for messages) and allow the body
to wrap rather than truncate, so longer action-oriented copy is fully readable.

Update the Tauri update toast to: sticky: true, ⬆ prefix on the title,
"Click to install and restart" as explicit call to action.

Fixes: auto-dismiss before user noticed it, no visual distinction from
a regular message notification.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/state/toast.ts

@@ -9,6 +9,7 @@ export type ToastNotif = {
   roomId: string;
   hashPath?: string; // overrides window.location.hash navigation when set
   onClick?: () => void; // custom click handler; skips hash navigation when set
+  sticky?: boolean; // when true, does not auto-dismiss — use for action toasts that require a click
 };
 
 const baseAtom = atom<ToastNotif[]>([]);