Add incremental belief updates and Laotzu variant

[Belzedar94]

Summary

• add incremental belief-state filtering with automatic rebuild triggers in the planner
• introduce Laotzu double-FRC darkcrazyhouse2 variant with randomized back ranks and startpos support
• document the completed FoW implementation steps and add a smoke test script for incremental fog-of-war search

Testing

• not run (not requested)

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Codex Task