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>

static/css/components/signal-cards.css

@@ -1020,6 +1020,8 @@
     display: flex;
     flex-direction: column;
     gap: 4px;
+    min-width: 0; /* Allow column to shrink in grid */
+    overflow: hidden;
 }
 
 .meter-aggregated-label {
@@ -1034,6 +1036,9 @@
     font-size: 16px;
     font-weight: 600;
     color: var(--text-primary);
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
 }
 
 /* Consumption column */
@@ -1068,6 +1073,8 @@
     min-height: 28px;
     display: flex;
     align-items: center;
+    max-width: 100%;
+    overflow: hidden;
 }
 
 .meter-sparkline-placeholder {
@@ -1082,6 +1089,9 @@
     font-size: 14px;
     font-weight: 500;
     color: var(--accent-cyan, #4a9eff);
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
 }
 
 /* Update animation */