fix(web): add shared DemSource singleton, add ErrorBoundary, and conditional view rendering to prevent WebGL crash

apps/web/src/pages/TacticalDefenseView.tsx

@@ -1,16 +1,7 @@
 import React, { useState, useEffect, useRef } from 'react';
 import maplibregl from 'maplibre-gl';
-import mlcontour from 'maplibre-contour';
-
-const demSource = new mlcontour.DemSource({
-  url: 'https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/{x}/{y}.png',
-  encoding: 'terrarium',
-  maxzoom: 15,
-  worker: true,
-  cacheSize: 100,
-});
-demSource.setupMaplibre(maplibregl);
 import 'maplibre-gl/dist/maplibre-gl.css';
+import { getSharedDemSource } from '../utils/demSource';
 import { 
   Shield, 
   Crosshair, 
@@ -456,6 +447,7 @@ export const TacticalDefenseView: React.FC = () => {
       });
 
       // Dynamic On-the-Fly Contours from Elevation DEM
+      const demSource = getSharedDemSource();
       const contourUrl = demSource.contourProtocolUrl({
         thresholds: {
           10: [100, 500],