v10.3.0

Add persistent notification support for device update progress

Summary

• The device can now create Home Assistant persistent notifications — used by the
  client for update progress: started, completed, no installer, or failure
• MQTT transport: new per-entry subscription on hass.agent/persistent_notification/{serial}
• HA API WebSocket transport: new hass_agent_persistent_notification event listener,
  filtered by serial number like the other WS events
• One notification ID per device (hass_agent_{serial}), so progress messages replace
  each other instead of piling up

Version

• 10.3.0 (stable) — fully backwards compatible: older clients simply never publish
  to the new topic/event, everything else works unchanged
• The notification feature activates with HASS.Agent .NET10 v10.3.0-beta.1 or newer
  on the Windows side