Run Webserver Start as a QGIS Background Task

Starting the embedded webserver currently blocks the QGIS UI thread for several seconds. This makes the plugin appear “frozen” during startup, which is confusing for end-users (especially non-technical staff).

QGIS provides a built-in mechanism for running long-running or blocking code in the background via QgsTask. Using a background task keeps the UI responsive and allows for clean progress or status messaging.

Proposed Solution

Move the webserver startup into a QGIS background task, similar to the existing Topology Check implementation:

def run_server_in_background(self) -> None:
    self.task = QgsTask.fromFunction(
        description="XMAS Webserver Start",
        function=self._start_server,
        on_finished=self._on_server_started,
    )

Reference: https://qgis.org/pyqgis/master/core/QgsTask.html#qgis.core.QgsTask.fromFunction

The task should:

• Execute the (blocking) server startup in the background
• Return success or failure back to the UI thread cleanly
• Optionally show a toast/notification (“Webserver started successfully”)
• Show user-friendly error feedback in case of failures
• Integrate with the existing task system used for run_topo_check_in_background

Acceptance Criteria

• QGIS remains fully responsive while the webserver starts
• No visible UI freeze or stutter
• Server starts reliably as before
• Clear success/error feedback to the user
• Code style matches the existing background task pattern