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/at-least-node/README.md

@@ -0,0 +1,25 @@
+# at-least-node
+
+![npm](https://img.shields.io/npm/v/at-least-node)
+![node](https://img.shields.io/node/v/at-least-node)
+![NPM](https://img.shields.io/npm/l/at-least-node)
+
+Sometimes you need to check if you're on _at least_ a given Node.js version, but you don't want to pull in the whole [`semver`](https://www.npmjs.com/package/semver) kitchen sink. That's what `at-least-node` is for.
+
+| Package         | Size    |
+| --------------- | ------- |
+| `at-least-node` | 2.6 kB  |
+| `semver`        | 75.5 kB |
+
+```js
+const atLeastNode = require('at-least-node')
+atLeastNode('10.12.0')
+// -> true on Node 10.12.0+, false on anything below that
+```
+
+When passing in a version string:
+
+- You cannot include a leading `v` (i.e. `v10.12.0`)
+- You cannot omit sections (i.e. `10.12`)
+- You cannot use pre-releases (i.e. `1.0.0-beta`)
+- There is no input validation, if you make a mistake, the resulting behavior is undefined