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/@surma/rollup-plugin-off-main-thread/karma.conf.js

@@ -0,0 +1,46 @@
+/**
+ * Copyright 2018 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module.exports = function(config) {
+  const configuration = {
+    basePath: "",
+    frameworks: ["mocha", "chai"],
+    files: [
+      {
+        pattern: "tests/fixtures/**",
+        included: false
+      },
+      {
+        pattern: "tests/*.test.js"
+      }
+    ],
+    reporters: ["progress"],
+    port: 9876,
+    colors: true,
+    logLevel: config.LOG_INFO,
+    autoWatch: true,
+    singleRun: true,
+    concurrency: 1,
+    browsers: ["Chrome", "Firefox", "Safari"],
+    customLaunchers: {
+      DockerChrome: {
+        base: "ChromeHeadless",
+        flags: ["--no-sandbox"]
+      }
+    }
+  };
+
+  if (process.env.INSIDE_DOCKER) configuration.browsers = ["DockerChrome"];
+
+  config.set(configuration);
+};