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/public/icons/generate-icons.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+# Generate simple SVG-based placeholder icons for the PWA
+# These should be replaced with proper icons later
+
+for size in 192 512; do
+  cat > "public/icons/icon-${size}.svg" << EOF
+<svg xmlns="http://www.w3.org/2000/svg" width="${size}" height="${size}" viewBox="0 0 ${size} ${size}">
+  <rect width="${size}" height="${size}" fill="#1A1A2E" rx="32"/>
+  <path d="M${size/2} ${size*15/100}L${size*15/100} ${size*55/100}h${size*15/100}v${size*30/100}h${size*40/100}v-${size*30/100}h${size*15/100}Z" fill="#FF6B35" stroke="#fff" stroke-width="${size/50}"/>
+  <text x="${size/2}" y="${size*75/100}" text-anchor="middle" fill="#fff" font-size="${size*15/100}" font-weight="bold" font-family="sans-serif">T</text>
+</svg>
+EOF
+done