eq: pass the real sample rate to eq-w0.py (fixes silent Graphic EQ)

Fixes #92

Problem

build/eq-w0.h is generated with 8 as the second argument to scripts/eq-w0.py, but eq-w0.py reads that argument as samples_per_sec:

• The Graphic EQ's biquad coefficients in audio/eq.h are then computed for an 8 Hz sample rate instead of the 48 kHz the audio path actually runs at.
• Result: garbage filter coefficients, so the effect outputs silence / garbage.

log2.py, pow2.py and quarter_sine.py take their 8 as a table-size step shift (2^8 = 256 entries), so the value is correct there. It was copied into the eq-w0.py rule by mistake.

Change

Makefile: pass the sample rate matching SAMPLES_PER_SEC (48000.0) in convert.c:

-	$(PYTHON) scripts/eq-w0.py build/eq-w0.h 8
+	$(PYTHON) scripts/eq-w0.py build/eq-w0.h 48000

Verification

scripts/eq-w0.py build/eq-w0.h 48000 now emits the expected header (// Precomputed EQ table for 48.000kHz sample rate) with sane per-octave coefficients instead of near-constant aliasing values.

Closes #92