feat(export): AIS UDP NMEA forward and JSON export endpoints for AIS/ADS-B

AIS:
- New optional NMEA UDP forwarding via AIS-catcher's -u flag, configurable
  from the AIS sidebar (host + port). Lets OpenCPN and other NMEA tools
  receive live vessel data directly. All SDR builders updated.
- New GET /ais/vessels endpoint — clean JSON snapshot of tracked vessels
  for REST integration

ADS-B:
- New GET /adsb/aircraft endpoint — JSON snapshot of all tracked aircraft,
  with optional ?icao= and ?military=true filters. Response includes a
  reminder that port 30003 (SBS) is already available for tools like
  Virtual Radar Server and OpenCPN's AIS/target plugin.

Closes #90

templates/partials/modes/ais.html

@@ -18,6 +18,23 @@
         </div>
     </div>
 
+    <div class="section">
+        <h3>NMEA UDP Forward</h3>
+        <p class="info-text" style="font-size: 11px; color: var(--text-dim); margin-bottom: 8px;">
+            Forward NMEA 0183 sentences to an external app (e.g. OpenCPN). Leave host blank to disable.
+        </p>
+        <div style="display: flex; gap: 8px;">
+            <div style="flex: 2;">
+                <label style="font-size: 10px; color: var(--text-dim);">Host</label>
+                <input type="text" id="aisUdpHost" placeholder="e.g. 192.168.1.10" style="width: 100%;">
+            </div>
+            <div style="flex: 1;">
+                <label style="font-size: 10px; color: var(--text-dim);">Port</label>
+                <input type="number" id="aisUdpPort" value="10110" min="1" max="65535" style="width: 100%;">
+            </div>
+        </div>
+    </div>
+
     <div class="section">
         <h3>Status</h3>
         <div id="aisStatusDisplay" class="info-text">
@@ -110,11 +127,22 @@
     function startAisTracking() {
         const gain = document.getElementById('aisGainInput').value || '40';
         const device = document.getElementById('deviceSelect')?.value || '0';
+        const udpHost = document.getElementById('aisUdpHost').value.trim();
+        const udpPort = parseInt(document.getElementById('aisUdpPort').value) || 10110;
+
+        const body = {
+            device, gain,
+            bias_t: typeof getBiasTEnabled === 'function' ? getBiasTEnabled() : false,
+        };
+        if (udpHost) {
+            body.udp_host = udpHost;
+            body.udp_port = udpPort;
+        }
 
         fetch('/ais/start', {
             method: 'POST',
             headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({ device, gain, bias_t: typeof getBiasTEnabled === 'function' ? getBiasTEnabled() : false })
+            body: JSON.stringify(body)
         })
         .then(r => r.json())
         .then(data => {