Fix multiple UI bugs and improve error handling

Issues fixed:
- #113: Display RTL-SDR serial numbers in device selector
- #112: Kill all processes now stops Bluetooth scans
- #111: BLE device list no longer overflows container bounds
- #109: WiFi scanner panels maintain minimum width (no more "imploding")
- #108: Radar device hover no longer causes violent shaking
- #106: "Use GPS" button now uses gpsd for USB GPS devices
- #105: Meter trend text no longer overlaps adjacent columns
- #104: dump1090 errors now provide specific troubleshooting guidance

Changes:
- app.py: Add Bluetooth cleanup to /killall endpoint
- routes/adsb.py: Parse dump1090 stderr for specific error messages
- templates/index.html: Show SDR serial numbers in device dropdown
- static/css/index.css: Fix WiFi/BT panel layouts with proper min-width
- static/css/components/signal-cards.css: Fix meter grid overflow
- static/css/components/proximity-viz.css: Fix radar hover transform
- static/css/settings.css: Add GPS detection spinner
- static/js/components/proximity-radar.js: Add invisible hit areas
- static/js/core/settings-manager.js: Use gpsd before browser geolocation

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

routes/adsb.py

@@ -732,16 +732,43 @@ def start_adsb():
                     stderr_output = app_module.adsb_process.stderr.read().decode('utf-8', errors='ignore').strip()
                 except Exception:
                     pass
-            if sdr_type == SDRType.RTL_SDR:
-                error_msg = 'dump1090 failed to start. Check RTL-SDR device permissions or if another process is using it.'
-                if stderr_output:
-                    error_msg += f' Error: {stderr_output[:200]}'
-                return jsonify({'status': 'error', 'message': error_msg})
+
+            # Parse stderr to provide specific guidance
+            error_type = 'START_FAILED'
+            stderr_lower = stderr_output.lower()
+
+            if 'usb_claim_interface' in stderr_lower or 'libusb_error_busy' in stderr_lower or 'device or resource busy' in stderr_lower:
+                error_msg = 'SDR device is busy. Another process may be using it.'
+                suggestion = 'Try: 1) Stop other SDR applications, 2) Run "pkill -f rtl_" to kill stale processes, or 3) Remove and reinsert the SDR device.'
+                error_type = 'DEVICE_BUSY'
+            elif 'no supported devices' in stderr_lower or 'no rtl-sdr' in stderr_lower or 'failed to open' in stderr_lower:
+                error_msg = 'RTL-SDR device not found.'
+                suggestion = 'Ensure the device is connected. Try removing and reinserting the SDR.'
+                error_type = 'DEVICE_NOT_FOUND'
+            elif 'kernel driver is active' in stderr_lower or 'dvb' in stderr_lower:
+                error_msg = 'Kernel DVB-T driver is blocking the device.'
+                suggestion = 'Blacklist the DVB drivers: Go to Settings > Hardware > "Blacklist DVB Drivers" or run "sudo rmmod dvb_usb_rtl28xxu".'
+                error_type = 'KERNEL_DRIVER'
+            elif 'permission' in stderr_lower or 'access' in stderr_lower:
+                error_msg = 'Permission denied accessing RTL-SDR device.'
+                suggestion = 'Run Intercept with sudo, or add udev rules for RTL-SDR devices.'
+                error_type = 'PERMISSION_DENIED'
+            elif sdr_type == SDRType.RTL_SDR:
+                error_msg = 'dump1090 failed to start.'
+                suggestion = 'Try removing and reinserting the SDR device, or check if another application is using it.'
             else:
-                error_msg = f'ADS-B decoder failed to start for {sdr_type.value}. Ensure readsb is installed with SoapySDR support and the device is connected.'
-                if stderr_output:
-                    error_msg += f' Error: {stderr_output[:200]}'
-                return jsonify({'status': 'error', 'message': error_msg})
+                error_msg = f'ADS-B decoder failed to start for {sdr_type.value}.'
+                suggestion = 'Ensure readsb is installed with SoapySDR support and the device is connected.'
+
+            full_msg = f'{error_msg} {suggestion}'
+            if stderr_output and len(stderr_output) < 300:
+                full_msg += f' (Details: {stderr_output})'
+
+            return jsonify({
+                'status': 'error',
+                'error_type': error_type,
+                'message': full_msg
+            })
 
         adsb_using_service = True
         adsb_active_device = device  # Track which device is being used