Add Airspy SDR support and persist GPS coordinates

Airspy support:
- Add AIRSPY to SDRType enum and driver mappings
- Create AirspyCommandBuilder using SoapySDR tools (rx_fm, readsb, rtl_433)
- Register in SDRFactory and add to hardware type dropdown
- Supports Airspy R2/Mini (24MHz-1.8GHz) and HF+ devices

GPS coordinate persistence:
- Save observer location to localStorage when manually entered or via geolocation
- Restore saved coordinates on page load in both index.html and adsb_dashboard.html
- Coordinates are shared between both pages

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

utils/sdr/__init__.py

@@ -30,6 +30,7 @@ from .detection import detect_all_devices
 from .rtlsdr import RTLSDRCommandBuilder
 from .limesdr import LimeSDRCommandBuilder
 from .hackrf import HackRFCommandBuilder
+from .airspy import AirspyCommandBuilder
 from .validation import (
     SDRValidationError,
     validate_frequency,
@@ -49,6 +50,7 @@ class SDRFactory:
         SDRType.RTL_SDR: RTLSDRCommandBuilder,
         SDRType.LIME_SDR: LimeSDRCommandBuilder,
         SDRType.HACKRF: HackRFCommandBuilder,
+        SDRType.AIRSPY: AirspyCommandBuilder,
     }
 
     @classmethod
@@ -214,6 +216,7 @@ __all__ = [
     'RTLSDRCommandBuilder',
     'LimeSDRCommandBuilder',
     'HackRFCommandBuilder',
+    'AirspyCommandBuilder',
     # Validation
     'SDRValidationError',
     'validate_frequency',