Improve Beast decoder with proper data formatting and altitude decoding

Major improvements to Beast message decoding and data presentation:

Speed & Track Formatting:
- Convert ground speed from float to integer (knots)
- Convert track angle from float to integer (0-359 degrees)
- Add proper rounding for velocity calculations
- Fix surface movement speed calculations

Altitude Decoding Enhancement:
- Implement proper Q-bit handling in altitude decoding
- Add altitude validation (range: -1000 to 60000 feet)
- Fix standard altitude encoding with 25-foot increments
- Add legacy Gray code support for older transponders
- Remove duplicate altitude values caused by incorrect decoding

ICAO Address Display:
- Fix JavaScript hex conversion that caused display corruption
- Remove duplicate toString(16) calls on already-formatted hex strings
- Proper ICAO display format (6-character hex like "4ACA0C")

Data Type Consistency:
- Update Aircraft struct to use integers for GroundSpeed and Track
- Update SpeedPoint struct for consistent integer speed/track storage
- Maintain float64 precision internally while displaying clean integers

Signal Strength:
- Confirm signal strength extraction is working properly
- Signal levels properly flow from Beast parser through merger to frontend
- Display in dBFS format (e.g., -1.57 dBFS)

Results:
- Clean integer speed values (198 kt instead of 238.03361107205006 kt)
- Proper track angles (41° instead of 37.83276127148023°)
- Realistic varying altitudes (1750-1825 ft instead of repeated 24450 ft)
- Correct ICAO formatting (4ACA0C instead of corrupted 103A)
- Working signal strength display (-0.98 to -2.16 dBFS)

The Beast decoder now produces accurate, properly formatted aircraft data
that displays cleanly in the web interface without data corruption.

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

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

assets/static/js/app.js

@@ -477,7 +477,7 @@ class SkyView {
     // Popup Content
     createPopupContent(aircraft) {
         const type = this.getAircraftType(aircraft);
-        const country = this.getCountryFromICAO(aircraft.ICAO24 ? aircraft.ICAO24.toString(16).toUpperCase() : '');
+        const country = this.getCountryFromICAO(aircraft.ICAO24 || '');
         const flag = this.getCountryFlag(country);
         
         const altitude = aircraft.Altitude || aircraft.BaroAltitude || 0;
@@ -499,7 +499,7 @@ class SkyView {
                 <div class="popup-header">
                     <div class="flight-info">
                         <span class="icao-flag">${flag}</span>
-                        <span class="flight-id">${aircraft.ICAO24 ? aircraft.ICAO24.toString(16).toUpperCase() : 'N/A'}</span>
+                        <span class="flight-id">${aircraft.ICAO24 || 'N/A'}</span>
                         ${aircraft.Callsign ? `→ <span class="callsign">${aircraft.Callsign}</span>` : ''}
                     </div>
                 </div>
@@ -611,7 +611,7 @@ class SkyView {
         if (searchTerm) {
             filteredData = filteredData.filter(aircraft =>
                 (aircraft.Callsign && aircraft.Callsign.toLowerCase().includes(searchTerm)) ||
-                (aircraft.ICAO24 && aircraft.ICAO24.toString(16).toLowerCase().includes(searchTerm)) ||
+                (aircraft.ICAO24 && aircraft.ICAO24.toLowerCase().includes(searchTerm)) ||
                 (aircraft.Squawk && aircraft.Squawk.includes(searchTerm))
             );
         }
@@ -638,7 +638,8 @@ class SkyView {
 
     createTableRow(aircraft) {
         const type = this.getAircraftType(aircraft);
-        const icao = aircraft.ICAO24 ? aircraft.ICAO24.toString(16).toUpperCase() : 'N/A';
+        // ICAO24 is already a hex string from the server
+        const icao = aircraft.ICAO24 || 'N/A';
         const altitude = aircraft.Altitude || aircraft.BaroAltitude || 0;
         const distance = this.calculateDistance(aircraft);
         const sources = aircraft.Sources ? Object.keys(aircraft.Sources).length : 0;
@@ -718,9 +719,9 @@ class SkyView {
                 case 'speed':
                     return (b.GroundSpeed || 0) - (a.GroundSpeed || 0);
                 case 'flight':
-                    return (a.Callsign || a.ICAO24?.toString(16) || '').localeCompare(b.Callsign || b.ICAO24?.toString(16) || '');
+                    return (a.Callsign || a.ICAO24 || '').localeCompare(b.Callsign || b.ICAO24 || '');
                 case 'icao':
-                    return (a.ICAO24?.toString(16) || '').localeCompare(b.ICAO24?.toString(16) || '');
+                    return (a.ICAO24 || '').localeCompare(b.ICAO24 || '');
                 case 'squawk':
                     return (a.Squawk || '').localeCompare(b.Squawk || '');
                 case 'signal':