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/path-key/index.d.ts

@@ -0,0 +1,40 @@
+/// <reference types="node" />
+
+declare namespace pathKey {
+	interface Options {
+		/**
+		Use a custom environment variables object. Default: [`process.env`](https://nodejs.org/api/process.html#process_process_env).
+		*/
+		readonly env?: {[key: string]: string | undefined};
+
+		/**
+		Get the PATH key for a specific platform. Default: [`process.platform`](https://nodejs.org/api/process.html#process_process_platform).
+		*/
+		readonly platform?: NodeJS.Platform;
+	}
+}
+
+declare const pathKey: {
+	/**
+	Get the [PATH](https://en.wikipedia.org/wiki/PATH_(variable)) environment variable key cross-platform.
+
+	@example
+	```
+	import pathKey = require('path-key');
+
+	const key = pathKey();
+	//=> 'PATH'
+
+	const PATH = process.env[key];
+	//=> '/usr/local/bin:/usr/bin:/bin'
+	```
+	*/
+	(options?: pathKey.Options): string;
+
+	// TODO: Remove this for the next major release, refactor the whole definition to:
+	// declare function pathKey(options?: pathKey.Options): string;
+	// export = pathKey;
+	default: typeof pathKey;
+};
+
+export = pathKey;