dsp/: C++ skeleton with working FFT/WOLA STFT

- Cooley-Tukey radix-2 FFT (forward + inverse with /N normalization)
- WOLA STFT/ISTFT with Hann window (nfft=2048, hop=512)
- WAV16 read + WAV24 write (fixed aliasing bug in read)
- Fixed in-place processing bug (separate input/output buffers)
- Biquad filter (peak/shelf/reject)
- Peak detector skeleton
- MS encode/decode (M8 stereo)
- Harness: WAV16 → STFT → WAV24 passthrough verified non-zero output

Verified: burst500.wav passthrough produces output RMS=0.0678

.gitignore

@@ -1,13 +1,17 @@
 # venv и тяжёлые/бинарные артефакты — в репо НЕ пушим
 *
-!*.py
-!*.txt
-!*.json
-!*.md
-!*.npy
-!*.npz
-!*.java
-!roadmap.md
+!**/*.py
+!**/*.txt
+!**/*.json
+!**/*.md
+!**/*.npy
+!**/*.npz
+!**/*.java
+!**/*.cpp
+!**/*.hpp
+!**/*.c
+!**/*.h
+!**/roadmap.md
 !.gitignore
 
 # тяжеловесы / чувствительные (исключены даже с include выше)