[fix](trx-backend-soapysdr): fine tune wfm phase trim

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -25,7 +25,7 @@ const PILOT_NOTCH_Q: f32 = 5.0;
 /// Narrow 19 kHz band-pass used to derive zero-crossings for switching stereo demod.
 const PILOT_BPF_Q: f32 = 20.0;
 /// Fixed phase trim on the recovered L-R channel.
-const STEREO_SEPARATION_PHASE_TRIM: f32 = 0.0;
+const STEREO_SEPARATION_PHASE_TRIM: f32 = 0.001;
 /// Fixed gain trim on the recovered L-R channel.
 const STEREO_SEPARATION_GAIN: f32 = 1.00;
 /// Extra headroom in the stereo matrix.