Application/Mode/Bandwidth API with OpusEncoder::with_application and
with_mode; SILK analysis-by-synthesis encoder mirroring the decoder's
fixed-point reconstruction with noise feedback, LTP, NLSF quantisation and
per-frame rate control; hybrid CELT from band 17 in the shared range coder;
pre-skip 120 in every mode. Oracle tests against filmcraft-opus and ffmpeg
(native opus + libopus).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>