Expose POST /api/audio/stereo-enhance and bass-enhance with 0–100 levels,
persist enhancements in AudioProfile, and document the virtual EQ mapping in
the manual and SigmaStudio chapter.
Co-authored-by: Cursor <cursoragent@cursor.com>
Document the ADAU1701 schematic chain (sigma-chain.jpg), cross-link from
hardware/firmware chapters, skip safeload on fixed high-pass band 0, and
match EqProfile default peaking frequencies to SigmaStudio.
Co-authored-by: Cursor <cursoragent@cursor.com>