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/@surma/rollup-plugin-off-main-thread/package.json

@@ -0,0 +1,36 @@
+{
+  "name": "@surma/rollup-plugin-off-main-thread",
+  "version": "2.2.3",
+  "description": "Use Rollup with workers and ES6 modules today.",
+  "main": "index.js",
+  "scripts": {
+    "fmt": "prettier --write 'tests/**/*.js' *.js *.md *.json",
+    "test": "node ./run_tests.js"
+  },
+  "author": "Surma <surma@google.com>",
+  "license": "Apache-2.0",
+  "devDependencies": {
+    "chai": "4.2.0",
+    "chalk": "^2.4.2",
+    "karma": "4.2.0",
+    "karma-chai": "0.1.0",
+    "karma-chrome-launcher": "3.0.0",
+    "karma-firefox-launcher": "1.1.0",
+    "karma-mocha": "1.3.0",
+    "karma-safari-launcher": "1.0.0",
+    "karma-safaritechpreview-launcher": "2.0.2",
+    "mocha": "6.1.4",
+    "prettier": "1.18.2",
+    "rollup": "2.2.0"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/surma/rollup-plugin-off-main-thread"
+  },
+  "dependencies": {
+    "ejs": "^3.1.6",
+    "json5": "^2.2.0",
+    "magic-string": "^0.25.0",
+    "string.prototype.matchall": "^4.0.6"
+  }
+}