Post-game analysis

Add a feature to the review mode that continues to analyse move strength. Start a background thread or process pool that analyses the moves from the displayed position and continuously updates the display. Consider adding the ability to explore new moves, or split that to a separate issue. Look at memory usage to decide how much of the search tree to save.

Start by locating the review mode and the existing move-analysis entry point for the displayed position. Define the scope first: continuous background analysis and display updates are requested, while exploring new moves may be separate; use memory usage to decide how much search-tree state to retain.

Written by the indexing model from the issue text.