Module tf_surface 

P7.5 — Time-frequency surface view over STFT/CQT rasters. P7.5 — Audio time-frequency SURFACE view over STFT/CQT rasters.

The existing audio::stft and audio::cqt_bake modules produce time × frequency magnitude rasters. This module treats those rasters as a 2D manifold surface where:

• u axis = time (frame index)
• v axis = frequency (bin index)
• height = magnitude (dB or linear)

The surface supports:

• Bilinear sampling at arbitrary (time, frequency) coordinates
• Gradient computation (spectral flux, frequency derivative)
• Ridge detection (local maxima along frequency axis per frame)
• Surface-to-mesh conversion for visualisation

Determinism

All operations are deterministic: the raster is a fixed f32 matrix, and sampling/gradient/ridge are pure functions.

Structs

TfSurface

A time-frequency surface: frames × bins magnitude raster.