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/tests/shelter-finder.test.ts

@@ -0,0 +1,70 @@
+import { describe, it, expect } from 'vitest';
+import { findNearest } from '../src/location/shelter-finder';
+import type { Shelter } from '../src/types';
+
+const shelters: Shelter[] = [
+  {
+    lokalId: 'a',
+    romnr: 1,
+    plasser: 100,
+    adresse: 'Near',
+    latitude: 59.91,
+    longitude: 10.75,
+  },
+  {
+    lokalId: 'b',
+    romnr: 2,
+    plasser: 200,
+    adresse: 'Mid',
+    latitude: 59.95,
+    longitude: 10.75,
+  },
+  {
+    lokalId: 'c',
+    romnr: 3,
+    plasser: 300,
+    adresse: 'Far',
+    latitude: 60.0,
+    longitude: 10.75,
+  },
+  {
+    lokalId: 'd',
+    romnr: 4,
+    plasser: 400,
+    adresse: 'Very Far',
+    latitude: 61.0,
+    longitude: 10.75,
+  },
+];
+
+describe('findNearest', () => {
+  it('returns shelters sorted by distance', () => {
+    const result = findNearest(shelters, 59.9, 10.75);
+    expect(result).toHaveLength(3);
+    expect(result[0].shelter.lokalId).toBe('a');
+    expect(result[1].shelter.lokalId).toBe('b');
+    expect(result[2].shelter.lokalId).toBe('c');
+  });
+
+  it('returns requested count', () => {
+    const result = findNearest(shelters, 59.9, 10.75, 2);
+    expect(result).toHaveLength(2);
+  });
+
+  it('returns all if fewer than count', () => {
+    const result = findNearest(shelters.slice(0, 1), 59.9, 10.75, 5);
+    expect(result).toHaveLength(1);
+  });
+
+  it('calculates distance and bearing', () => {
+    const result = findNearest(shelters, 59.9, 10.75, 1);
+    expect(result[0].distanceMeters).toBeGreaterThan(0);
+    expect(result[0].bearingDegrees).toBeGreaterThanOrEqual(0);
+    expect(result[0].bearingDegrees).toBeLessThan(360);
+  });
+
+  it('handles empty shelter list', () => {
+    const result = findNearest([], 59.9, 10.75);
+    expect(result).toHaveLength(0);
+  });
+});