Add configurable beam width for beam search

[IliaGodlevsky]

Summary

• add a dedicated beam width view for run creation and bind it to the run creation view model
• plumb the selected beam width through algorithm build info and into the beam search factory
• allow the beam search algorithm to accept a configurable beam width rather than a hardcoded limit

Testing

• dotnet build Pathfinding.sln (fails: command not found)

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https://chatgpt.com/codex/tasks/task_e_690541bed9108333a4ed218e4d0e20b7