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/helpers/valueToFloat32Bytes.js

@@ -0,0 +1,67 @@
+'use strict';
+
+var $abs = require('math-intrinsics/abs');
+var $floor = require('math-intrinsics/floor');
+var $pow = require('math-intrinsics/pow');
+
+var isFinite = require('math-intrinsics/isFinite');
+var isNaN = require('math-intrinsics/isNaN');
+var isNegativeZero = require('math-intrinsics/isNegativeZero');
+
+var maxFiniteFloat32 = 3.4028234663852886e+38; // roughly 2 ** 128 - 1
+
+module.exports = function valueToFloat32Bytes(value, isLittleEndian) {
+	if (isNaN(value)) {
+		return isLittleEndian ? [0, 0, 192, 127] : [127, 192, 0, 0]; // hardcoded
+	}
+
+	var leastSig;
+
+	if (value === 0) {
+		leastSig = isNegativeZero(value) ? 0x80 : 0;
+		return isLittleEndian ? [0, 0, 0, leastSig] : [leastSig, 0, 0, 0];
+	}
+
+	if ($abs(value) > maxFiniteFloat32 || !isFinite(value)) {
+		leastSig = value < 0 ? 255 : 127;
+		return isLittleEndian ? [0, 0, 128, leastSig] : [leastSig, 128, 0, 0];
+	}
+
+	var sign = value < 0 ? 1 : 0;
+	value = $abs(value); // eslint-disable-line no-param-reassign
+
+	var exponent = 0;
+	while (value >= 2) {
+		exponent += 1;
+		value /= 2; // eslint-disable-line no-param-reassign
+	}
+
+	while (value < 1) {
+		exponent -= 1;
+		value *= 2; // eslint-disable-line no-param-reassign
+	}
+
+	var mantissa = value - 1;
+	mantissa *= $pow(2, 23) + 0.5;
+	mantissa = $floor(mantissa);
+
+	exponent += 127;
+	exponent <<= 23;
+
+	var result = (sign << 31)
+        | exponent
+        | mantissa;
+
+	var byte0 = result & 255;
+	result >>= 8;
+	var byte1 = result & 255;
+	result >>= 8;
+	var byte2 = result & 255;
+	result >>= 8;
+	var byte3 = result & 255;
+
+	if (isLittleEndian) {
+		return [byte0, byte1, byte2, byte3];
+	}
+	return [byte3, byte2, byte1, byte0];
+};