fix: avoid spamming NewToolTip D-Bus signals on Wayland

[Artt4]

Problem

checkDownloadInfo() runs every 200 ms and unconditionally calls QSystemTrayIcon.setToolTip(). On Wayland, Qt's StatusNotifierItem backend emits a NewToolTip D-Bus signal on every call, flooding the session bus with ~5 signals per second even when no downloads are active.

This causes SNI-based tray hosts such as Waybar to stop displaying tooltips for all tray items while Persepolis is running.

Fix

Only call setToolTip() when the tooltip text has actually changed. This keeps the download-progress tooltip working but eliminates the redundant D-Bus traffic.

Testing

• Run Persepolis from source with python3 ./test/test.py.
• Monitor D-Bus:

timeout 3 dbus-monitor --session "type='signal',interface='org.kde.StatusNotifierItem',member='NewToolTip'" 2>/dev/null | grep -c 'NewToolTip'

- Before: ~15 signals in 3 seconds.
- After: 0–1 signals when idle; updates only when download progress changes.