feat: Add VHF DSC Channel 70 monitoring and decoding

- Implement DSC message decoding (Distress, Urgency, Safety, Routine)

- Add MMSI country identification via MID lookup

- Integrate position extraction and map markers for distress alerts

- Implement device conflict detection to prevent SDR collisions with AIS

- Add permanent storage for critical alerts and visual UI overlays

utils/dsc/__init__.py

@@ -0,0 +1,34 @@
+"""
+DSC (Digital Selective Calling) utilities.
+
+VHF DSC is a maritime distress and safety calling system operating on 156.525 MHz
+(VHF Channel 70). It provides automated calling for distress, urgency, safety,
+and routine communications per ITU-R M.493.
+"""
+
+from .constants import (
+    FORMAT_CODES,
+    DISTRESS_NATURE_CODES,
+    TELECOMMAND_CODES,
+    CATEGORY_PRIORITY,
+    MID_COUNTRY_MAP,
+)
+
+from .parser import (
+    parse_dsc_message,
+    get_country_from_mmsi,
+    get_distress_nature_text,
+    get_format_text,
+)
+
+__all__ = [
+    'FORMAT_CODES',
+    'DISTRESS_NATURE_CODES',
+    'TELECOMMAND_CODES',
+    'CATEGORY_PRIORITY',
+    'MID_COUNTRY_MAP',
+    'parse_dsc_message',
+    'get_country_from_mmsi',
+    'get_distress_nature_text',
+    'get_format_text',
+]