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/workbox-routing/utils/constants.js

@@ -0,0 +1,32 @@
+/*
+  Copyright 2018 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import '../_version.js';
+/**
+ * The default HTTP method, 'GET', used when there's no specific method
+ * configured for a route.
+ *
+ * @type {string}
+ *
+ * @private
+ */
+export const defaultMethod = 'GET';
+/**
+ * The list of valid HTTP methods associated with requests that could be routed.
+ *
+ * @type {Array<string>}
+ *
+ * @private
+ */
+export const validMethods = [
+    'DELETE',
+    'GET',
+    'HEAD',
+    'PATCH',
+    'POST',
+    'PUT',
+];