secondary-sdr: AIS-catcher output flag is -o 5, not -o JSON

AIS-catcher rejects '-o JSON' (Unknown message format) and exited on
every index. -o 5 is JSON Full, whose field names the reader already
expects. Verified on radio-box: 16 AIS transmitters (Hudson AtoN buoys)
decoded on a 9cm whip. (node-26#9)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

secondary-sdr-container/app/internal/decoder_control.py

@@ -86,7 +86,7 @@ def _ais_command(index: int) -> List[str]:
     return [
         "/opt/AIS-catcher/build/AIS-catcher",
         f"-d:{index}",  # "-d <x>" would select by serial, not index
-        "-o", "JSON",
+        "-o", "5",  # JSON Full: decoded fields (4 = sparse, "JSON" is rejected)
     ]