Fix DCA-derived IBIT zscore settings

[Pigbibi]

Summary

• remove the website IBIT Z-Score exit selector and legacy account sync setting
• derive IBIT Z-Score runtime/plugin settings from ibit_smart_dca smart DCA mode
• restrict DCA controls to IBIT and Nasdaq/S&P DCA strategies; BTC DCA no longer enables DCA settings

Validation

• node tests/strategy_switch_worker_validation.mjs
• python3 -m unittest python.tests.test_runtime_settings
• python3 python/scripts/build_config.py --check
• node/python syntax checks and git diff --check
• local browser mock validation for IBIT smart DCA and BTC DCA disabled controls

[github-actions]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Honor preserved smart DCA when deriving IBIT Z-score

When an IBIT account already has DCA_MODE=smart and the dispatch omits DCA controls (for example, a manual run that only changes reserved cash or execution mode), this defaults effective_dca_mode to fixed before reading/preserving the existing variable. Later _dca_extra_variables omits DCA_MODE, so _preserve_reserved_cash_fields keeps the old smart DCA value, but the plugin mounts, scheduler, and IBIT_ZSCORE_EXIT_* variables were generated for fixed mode, leaving a smart-DCA account with the z-score plugin disabled and the monthly scheduler. Derive this from the current/preserved DCA setting or require the DCA control whenever these derived settings are recomputed.

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