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/is-stream/index.d.ts

@@ -0,0 +1,79 @@
+import * as stream from 'stream';
+
+declare const isStream: {
+	/**
+	@returns Whether `stream` is a [`Stream`](https://nodejs.org/api/stream.html#stream_stream).
+
+	@example
+	```
+	import * as fs from 'fs';
+	import isStream = require('is-stream');
+
+	isStream(fs.createReadStream('unicorn.png'));
+	//=> true
+
+	isStream({});
+	//=> false
+	```
+	*/
+	(stream: unknown): stream is stream.Stream;
+
+	/**
+	@returns Whether `stream` is a [`stream.Writable`](https://nodejs.org/api/stream.html#stream_class_stream_writable).
+
+	@example
+	```
+	import * as fs from 'fs';
+	import isStream = require('is-stream');
+
+	isStream.writable(fs.createWriteStrem('unicorn.txt'));
+	//=> true
+	```
+	*/
+	writable(stream: unknown): stream is stream.Writable;
+
+	/**
+	@returns Whether `stream` is a [`stream.Readable`](https://nodejs.org/api/stream.html#stream_class_stream_readable).
+
+	@example
+	```
+	import * as fs from 'fs';
+	import isStream = require('is-stream');
+
+	isStream.readable(fs.createReadStream('unicorn.png'));
+	//=> true
+	```
+	*/
+	readable(stream: unknown): stream is stream.Readable;
+
+	/**
+	@returns Whether `stream` is a [`stream.Duplex`](https://nodejs.org/api/stream.html#stream_class_stream_duplex).
+
+	@example
+	```
+	import {Duplex} from 'stream';
+	import isStream = require('is-stream');
+
+	isStream.duplex(new Duplex());
+	//=> true
+	```
+	*/
+	duplex(stream: unknown): stream is stream.Duplex;
+
+	/**
+	@returns Whether `stream` is a [`stream.Transform`](https://nodejs.org/api/stream.html#stream_class_stream_transform).
+
+	@example
+	```
+	import * as fs from 'fs';
+	import Stringify = require('streaming-json-stringify');
+	import isStream = require('is-stream');
+
+	isStream.transform(Stringify());
+	//=> true
+	```
+	*/
+	transform(input: unknown): input is stream.Transform;
+};
+
+export = isStream;