Add progressive web app companion for cross-platform access

Vite + TypeScript PWA that mirrors the Android app's core features:
- Pre-processed shelter data (build-time UTM33N→WGS84 conversion)
- Leaflet map with shelter markers, user location, and offline tiles
- Canvas compass arrow (ported from DirectionArrowView.kt)
- IndexedDB shelter cache with 7-day staleness check
- Service worker with CacheFirst tiles and precached app shell
- i18n for en, nb, nn (ported from Android strings.xml)
- iOS/Android compass handling with low-pass filter
- Respects user map interaction (no auto-snap on pan/zoom)
- Build revision cache-breaker for reliable SW updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pwa/node_modules/lodash/subtract.js

@@ -0,0 +1,22 @@
+var createMathOperation = require('./_createMathOperation');
+
+/**
+ * Subtract two numbers.
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category Math
+ * @param {number} minuend The first number in a subtraction.
+ * @param {number} subtrahend The second number in a subtraction.
+ * @returns {number} Returns the difference.
+ * @example
+ *
+ * _.subtract(6, 4);
+ * // => 2
+ */
+var subtract = createMathOperation(function(minuend, subtrahend) {
+  return minuend - subtrahend;
+}, 0);
+
+module.exports = subtract;