OptionsForm now shows checkboxes for each fill strategy, persisted via
the new DisabledStrategies user setting. FillStrategyRegistry exposes
AllStrategies and DisabledNames for the UI. MainForm applies disabled
strategies on startup via OptionsForm.ApplyDisabledStrategies().
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>