[fix](trx-backend-soapysdr): raise wfm stereo matrix gain to unity

Output gain clamp catches any peaks from full-deviation signals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/trx-backend/trx-backend-soapysdr/src/demod.rs

@@ -33,7 +33,7 @@ const STEREO_SEPARATION_PHASE_TRIM: f32 = 0.0;
 const STEREO_SEPARATION_GAIN: f32 = 1.000;
 /// Extra headroom in the stereo matrix to reduce stereo-only clipping/IMD on
 /// strong program material. This keeps bass excursions from flattening treble.
-const STEREO_MATRIX_GAIN: f32 = 0.80;
+const STEREO_MATRIX_GAIN: f32 = 1.00;
 /// Stereo detection runs every N composite samples to reduce CPU.
 const STEREO_DETECT_DECIMATION: u32 = 16;
 /// Gentle high-pass memory for the stereo L-R path.