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/source-map-js/lib/base64.js

@@ -0,0 +1,67 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2011 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ */
+
+var intToCharMap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('');
+
+/**
+ * Encode an integer in the range of 0 to 63 to a single base 64 digit.
+ */
+exports.encode = function (number) {
+  if (0 <= number && number < intToCharMap.length) {
+    return intToCharMap[number];
+  }
+  throw new TypeError("Must be between 0 and 63: " + number);
+};
+
+/**
+ * Decode a single base 64 character code digit to an integer. Returns -1 on
+ * failure.
+ */
+exports.decode = function (charCode) {
+  var bigA = 65;     // 'A'
+  var bigZ = 90;     // 'Z'
+
+  var littleA = 97;  // 'a'
+  var littleZ = 122; // 'z'
+
+  var zero = 48;     // '0'
+  var nine = 57;     // '9'
+
+  var plus = 43;     // '+'
+  var slash = 47;    // '/'
+
+  var littleOffset = 26;
+  var numberOffset = 52;
+
+  // 0 - 25: ABCDEFGHIJKLMNOPQRSTUVWXYZ
+  if (bigA <= charCode && charCode <= bigZ) {
+    return (charCode - bigA);
+  }
+
+  // 26 - 51: abcdefghijklmnopqrstuvwxyz
+  if (littleA <= charCode && charCode <= littleZ) {
+    return (charCode - littleA + littleOffset);
+  }
+
+  // 52 - 61: 0123456789
+  if (zero <= charCode && charCode <= nine) {
+    return (charCode - zero + numberOffset);
+  }
+
+  // 62: +
+  if (charCode == plus) {
+    return 62;
+  }
+
+  // 63: /
+  if (charCode == slash) {
+    return 63;
+  }
+
+  // Invalid base64 digit.
+  return -1;
+};