Add notifications for completed tasks and approval-required turns.

[sbansal1999]

Right now if a task finishes in a chat while the user is in another app, they get no signal. Same for approval-required turns in supervised mode.

We should notify users when:

• a task/turn completes
• an approval is required in supervised mode

[yehyal]

I started working on an mvp for this issue for the task completion part, team let me know if this is something you will consider and if I should open a PR

[obrunogonzaga]

I’d like to work on a small, focused version of this.

I reviewed #976, #1657, #1780, and the notification-sound foundation in #2373. My proposed scope would be limited to native OS notifications when T3 Code is not focused:

• turn completed
• approval or user input required
• turn failed
• click opens the relevant thread
• opt-in and disabled by default

No sounds, overlays, pets, tray UI, or broader lifecycle-hook system.

Would this scope be welcome if built on the newer thread-state foundation, or would you prefer to wait for #2373 first?

[tsatsujnr139]

@obrunogonzaga Is there any movement on your PR? I was looking to file a similar issue and came across this.