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/isexe/README.md

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+# isexe
+
+Minimal module to check if a file is executable, and a normal file.
+
+Uses `fs.stat` and tests against the `PATHEXT` environment variable on
+Windows.
+
+## USAGE
+
+```javascript
+var isexe = require('isexe')
+isexe('some-file-name', function (err, isExe) {
+  if (err) {
+    console.error('probably file does not exist or something', err)
+  } else if (isExe) {
+    console.error('this thing can be run')
+  } else {
+    console.error('cannot be run')
+  }
+})
+
+// same thing but synchronous, throws errors
+var isExe = isexe.sync('some-file-name')
+
+// treat errors as just "not executable"
+isexe('maybe-missing-file', { ignoreErrors: true }, callback)
+var isExe = isexe.sync('maybe-missing-file', { ignoreErrors: true })
+```
+
+## API
+
+### `isexe(path, [options], [callback])`
+
+Check if the path is executable.  If no callback provided, and a
+global `Promise` object is available, then a Promise will be returned.
+
+Will raise whatever errors may be raised by `fs.stat`, unless
+`options.ignoreErrors` is set to true.
+
+### `isexe.sync(path, [options])`
+
+Same as `isexe` but returns the value and throws any errors raised.
+
+### Options
+
+* `ignoreErrors` Treat all errors as "no, this is not executable", but
+  don't raise them.
+* `uid` Number to use as the user id
+* `gid` Number to use as the group id
+* `pathExt` List of path extensions to use instead of `PATHEXT`
+  environment variable on Windows.