feat: bridge imageflow quality system to zen with_generic_quality() #717

Summary

Replace imageflow's QUALITY_HINTS table and QualityProfileHints struct in auto.rs with direct calls to config.with_generic_quality(). Each zen codec has its own 26-anchor calibration table that is more accurate than imageflow's 8-anchor centralized table.

Changes

• Delete QUALITY_HINTS, QualityProfileHints, get_quality_hints(), get_quality_hints_with_dpr(), get_quality_hints_by_ssim2() from auto.rs
• QualityProfile::Percent(f32) passes through directly
• Named profiles map via generic_quality() (same anchor values: 15/20/34/55/73/91/96/100)
• Wire EncodeSpeed presets through RIAPI (new speed= querystring key)

Dependencies

• DPR reconciliation: fix: reconcile DPR quality adjustment formula zenpipe#31
• EncodeSpeed presets: feat: add EncodeSpeed presets (Fastest / Realtime / Offline / OfflineMax) zenpipe#28