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/es-abstract/2024/ToInt32.js

@@ -0,0 +1,23 @@
+'use strict';
+
+var modulo = require('./modulo');
+var ToNumber = require('./ToNumber');
+var truncate = require('./truncate');
+
+var isFinite = require('math-intrinsics/isFinite');
+
+// https://262.ecma-international.org/14.0/#sec-toint32
+
+var two31 = 0x80000000; // Math.pow(2, 31);
+var two32 = 0x100000000; // Math.pow(2, 32);
+
+module.exports = function ToInt32(argument) {
+	var number = ToNumber(argument);
+	if (!isFinite(number) || number === 0) {
+		return 0;
+	}
+	var int = truncate(number);
+	var int32bit = modulo(int, two32);
+	var result = int32bit >= two31 ? int32bit - two32 : int32bit;
+	return result === 0 ? 0 : result; // in the spec, these are math values, so we filter out -0 here
+};