Feat: Notifications

[leobrqz]

Idea: When a scheduled script starts, stops, fails, exits non‑zero or exceeds a threshold (like runtime > 30 min, or RAM > 1 GB etc), the app can notify: system tray, desktop notification, or webhook (Slack, Discord, custom URL = unlikely tho).

Config: per schedule or global (“notify on any failure”, "notify on start and/or stop) with simple rules (only if status = failed or exit ≠ 0).

I gotta see how this could be done on Qt