fix: Correct SSTV VIS codes and replace Goertzel pixel decoder with Hilbert transform

Fix wrong VIS codes for PD90 (96→99), PD120 (93→95), PD180 (95→97),
PD240 (113→96), and ScottieDX (55→76). This caused PD180 to be detected
as PD90 and PD120 to fail entirely.

Replace batch Goertzel pixel decoding with analytic signal (Hilbert
transform) FM demodulation. The Goertzel approach used 96-sample windows
with ~500 Hz resolution — wider than the 800 Hz pixel frequency range —
making accurate pixel decoding impossible for fast modes like Martin2
and Scottie2. The Hilbert method computes per-sample instantaneous
frequency, matching the approach used by QSSTV and other professional
SSTV decoders.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

utils/sstv/constants.py

@@ -59,15 +59,15 @@ VIS_CODES: dict[int, str] = {
     40:  'Martin2',
     60:  'Scottie1',
     56:  'Scottie2',
-    93:  'PD120',
-    95:  'PD180',
+    95:  'PD120',
+    97:  'PD180',
     # Less common but recognized
     4:   'Robot24',
     36:  'Martin3',
     52:  'Scottie3',
-    55:  'ScottieDX',
-    113: 'PD240',
-    96:  'PD90',
+    76:  'ScottieDX',
+    96:  'PD240',
+    99:  'PD90',
     98:  'PD160',
 }