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/tests/import-worker-url.test.js

@@ -0,0 +1,41 @@
+/**
+ * Copyright 2020 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.
+ */
+
+describe("omt: URL import", function() {
+  const runner = "/base/tests/fixtures/import-worker-url/build/runner.html";
+
+  beforeEach(function() {
+    this.ifr = document.createElement("iframe");
+    document.body.append(this.ifr);
+  });
+
+  afterEach(function() {
+    this.ifr.remove();
+  });
+
+  it("imports as string", async function() {
+    this.ifr.src = runner;
+    await new Promise(resolve => this.ifr.addEventListener("load", resolve));
+    assert.typeOf(this.ifr.contentWindow.workerURL, "string");
+  });
+
+  it("loads transpiled modules", function(done) {
+    window.addEventListener("message", function l(ev) {
+      if (ev.data === "a") {
+        window.removeEventListener("message", l);
+        done();
+      }
+    });
+    this.ifr.src = runner;
+  });
+});