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/postcss/lib/document.js

@@ -0,0 +1,33 @@
+'use strict'
+
+let Container = require('./container')
+
+let LazyResult, Processor
+
+class Document extends Container {
+  constructor(defaults) {
+    // type needs to be passed to super, otherwise child roots won't be normalized correctly
+    super({ type: 'document', ...defaults })
+
+    if (!this.nodes) {
+      this.nodes = []
+    }
+  }
+
+  toResult(opts = {}) {
+    let lazy = new LazyResult(new Processor(), this, opts)
+
+    return lazy.stringify()
+  }
+}
+
+Document.registerLazyResult = dependant => {
+  LazyResult = dependant
+}
+
+Document.registerProcessor = dependant => {
+  Processor = dependant
+}
+
+module.exports = Document
+Document.default = Document