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/why-is-node-running/cli.js

@@ -0,0 +1,18 @@
+#!/usr/bin/env node
+
+var spawn = require('child_process').spawn
+var path = require('path')
+
+var prog = path.resolve(process.argv[2])
+var progArgs = process.argv.slice(3)
+
+console.log('probing program', prog)
+
+var nodeArgs = [
+  '-r',
+  path.join(__dirname, 'include.js')
+]
+var nodeOpts = { stdio: 'inherit' }
+var child = spawn('node', nodeArgs.concat(prog).concat(progArgs), nodeOpts)
+
+console.log('kill -SIGUSR1', child.pid, 'for logging')