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/core-js-compat/compat.js

@@ -0,0 +1,90 @@
+'use strict';
+const { compare, filterOutStabilizedProposals, has, intersection } = require('./helpers');
+const data = require('./data');
+const entries = require('./entries');
+const getModulesListForTargetVersion = require('./get-modules-list-for-target-version');
+const allModules = require('./modules');
+const targetsParser = require('./targets-parser');
+
+function throwInvalidFilter(filter) {
+  throw new TypeError(`Specified invalid module name or pattern: ${ filter }`);
+}
+
+function atLeastSomeModules(modules, filter) {
+  if (!modules.length) throwInvalidFilter(filter);
+  return modules;
+}
+
+function getModules(filter) {
+  if (typeof filter == 'string') {
+    if (has(entries, filter)) return entries[filter];
+    return atLeastSomeModules(allModules.filter(it => it.startsWith(filter)), filter);
+  }
+  if (filter instanceof RegExp) return atLeastSomeModules(allModules.filter(it => filter.test(it)), filter);
+  throwInvalidFilter(filter);
+}
+
+function normalizeModules(option) {
+  // TODO: use `.flatMap` in core-js@4
+  return new Set(Array.isArray(option) ? [].concat(...option.map(getModules)) : getModules(option));
+}
+
+function checkModule(name, targets) {
+  const result = {
+    required: !targets,
+    targets: {},
+  };
+
+  if (!targets) return result;
+
+  const requirements = data[name];
+
+  for (const [engine, version] of targets) {
+    if (!has(requirements, engine) || compare(version, '<', requirements[engine])) {
+      result.required = true;
+      result.targets[engine] = version;
+    }
+  }
+
+  return result;
+}
+
+module.exports = function ({
+  filter = null, // TODO: Obsolete, remove from `core-js@4`
+  modules = null,
+  exclude = [],
+  targets = null,
+  version = null,
+  inverse = false,
+} = {}) {
+  if (modules === null || modules === undefined) modules = filter;
+  inverse = !!inverse;
+
+  const parsedTargets = targets ? targetsParser(targets) : null;
+
+  const result = {
+    list: [],
+    targets: {},
+  };
+
+  exclude = normalizeModules(exclude);
+
+  modules = modules ? [...normalizeModules(modules)] : allModules;
+
+  if (exclude.size) modules = modules.filter(it => !exclude.has(it));
+
+  modules = intersection(modules, version ? getModulesListForTargetVersion(version) : allModules);
+
+  if (!inverse) modules = filterOutStabilizedProposals(modules);
+
+  for (const key of modules) {
+    const check = checkModule(key, parsedTargets);
+
+    if (check.required ^ inverse) {
+      result.list.push(key);
+      result.targets[key] = check.targets;
+    }
+  }
+
+  return result;
+};