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/nanoid/non-secure/index.d.ts

@@ -0,0 +1,33 @@
+/**
+ * Generate URL-friendly unique ID. This method uses the non-secure
+ * predictable random generator with bigger collision probability.
+ *
+ * ```js
+ * import { nanoid } from 'nanoid/non-secure'
+ * model.id = nanoid() //=> "Uakgb_J5m9g-0JDMbcJqL"
+ * ```
+ *
+ * @param size Size of the ID. The default size is 21.
+ * @returns A random string.
+ */
+export function nanoid(size?: number): string
+
+/**
+ * Generate a unique ID based on a custom alphabet.
+ * This method uses the non-secure predictable random generator
+ * with bigger collision probability.
+ *
+ * @param alphabet Alphabet used to generate the ID.
+ * @param defaultSize Size of the ID. The default size is 21.
+ * @returns A random string generator.
+ *
+ * ```js
+ * import { customAlphabet } from 'nanoid/non-secure'
+ * const nanoid = customAlphabet('0123456789абвгдеё', 5)
+ * model.id = //=> "8ё56а"
+ * ```
+ */
+export function customAlphabet(
+  alphabet: string,
+  defaultSize?: number
+): (size?: number) => string