Replace driver_type filter with Sd-based frequency capability estimate

[timini]

Summary

• Replace the blanket driver_type string filter in prescreen that excluded all cone drivers when target_f_high > 2kHz
• New filter computes pistonic beaming frequency from Sd (f_piston = c / (2π·√(Sd/π))) and multiplies by a configurable horn_load_factor (default 10×) to estimate horn-loaded upper frequency limit
• Adds --horn-load-factor CLI argument for tuning the extension factor
• 6" and 8" cone mids now correctly pass for mid-horn applications (250–6.5 kHz), while 10"+ woofers are still rejected

Test plan

• All 12 prescreen unit tests pass (updated for new physics-based filter)
• Run prescreen CLI with 250–6500 Hz target, verify 6"/8" cone mids + compression drivers pass
• Run prescreen CLI with 40–500 Hz bass target, verify large cone drivers pass

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