Add VRS JSON format support for readsb integration

Added comprehensive support for VRS (Virtual Radar Server) JSON format
as a simpler alternative to Beast binary protocol, enabling integration
with readsb --net-vrs-port output.

## Key Features:
- **VRS JSON Parser**: Stream parsing of newline-delimited JSON aircraft data
- **VRS Client**: TCP client with automatic reconnection and error recovery
- **Mixed Format Support**: Use Beast and VRS sources simultaneously
- **Enhanced Aircraft Data**: Added VRS-specific fields (registration, type, operator)
- **Position Source Tracking**: Identifies ADS-B, MLAT, TIS-B, and satellite positions

## Implementation:
- `internal/vrs/parser.go`: VRS JSON message parsing and validation
- `internal/client/vrs.go`: VRS TCP client implementation
- Enhanced `MultiSourceClient` to support both Beast and VRS formats
- Extended `Aircraft` struct with validity flags and additional metadata
- Updated configuration to include `format` field ("beast" or "vrs")

## Testing:
- Successfully tested against svovel:33005 VRS JSON stream
- Verified aircraft data parsing and position tracking
- Confirmed mixed-format operation with existing Beast clients

## Documentation:
- Updated README.md with VRS format configuration examples
- Enhanced ARCHITECTURE.md with VRS parser documentation
- Added data format comparison and configuration guide

This enables simpler integration with modern readsb installations while
maintaining full backward compatibility with existing Beast deployments.

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

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

vrs-test-config.json

@@ -0,0 +1,29 @@
+{
+  "server": {
+    "host": "",
+    "port": 8080
+  },
+  "sources": [
+    {
+      "id": "svovel-vrs",
+      "name": "Svovel VRS JSON",
+      "host": "svovel",
+      "port": 33005,
+      "format": "vrs",
+      "latitude": 60.0,
+      "longitude": 10.0,
+      "altitude": 100.0,
+      "enabled": true
+    }
+  ],
+  "settings": {
+    "history_limit": 500,
+    "stale_timeout": 60,
+    "update_rate": 1
+  },
+  "origin": {
+    "latitude": 60.0,
+    "longitude": 10.0,
+    "name": "Oslo Area"
+  }
+}