notif act/dismiss should mark GitHub threads done upstream

[blink-claw-bot]

Problem

argus notif act and argus notif dismiss update the local SQLite row, but they do not update the upstream GitHub notification thread. That leaves a split-brain state: Argus says the notification is handled, while GitHub may still show it as unread/inbox/done-state pending depending on the user's notification UI/API view.

Relevant code:

• cmd_notif_act updates notifications.acted_at and logs activity, then returns.
• cmd_notif_dismiss sets dismissed = 1 and logs activity, then returns.

Suggested behavior

When a notification is explicitly acted or dismissed, mark the GitHub thread as Done too.

GitHub's REST API distinguishes read vs done:

• PATCH /notifications/threads/{thread_id} = read
• DELETE /notifications/threads/{thread_id} = done

Implementation hint

Add a small helper and call it from both cmd_notif_act and cmd_notif_dismiss for the gh backend:

def gh_mark_thread_done(notif_id: str) -> bool:
    result = subprocess.run(
        ["gh", "api", "--method", "DELETE", f"notifications/threads/{notif_id}"],
        capture_output=True,
        text=True,
    )
    if result.returncode != 0:
        print(f"Warning: failed to mark GitHub notification done: {result.stderr}", file=sys.stderr)
        return False
    return True

Do not delete /subscription for normal done handling; unsubscribing can suppress future useful notifications on that thread.