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/ajv/lib/runtime/timestamp.ts

@@ -0,0 +1,46 @@
+const DT_SEPARATOR = /t|\s/i
+const DATE = /^(\d\d\d\d)-(\d\d)-(\d\d)$/
+const TIME = /^(\d\d):(\d\d):(\d\d)(?:\.\d+)?(?:z|([+-]\d\d)(?::?(\d\d))?)$/i
+const DAYS = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+
+export default function validTimestamp(str: string, allowDate: boolean): boolean {
+  // http://tools.ietf.org/html/rfc3339#section-5.6
+  const dt: string[] = str.split(DT_SEPARATOR)
+  return (
+    (dt.length === 2 && validDate(dt[0]) && validTime(dt[1])) ||
+    (allowDate && dt.length === 1 && validDate(dt[0]))
+  )
+}
+
+function validDate(str: string): boolean {
+  const matches: string[] | null = DATE.exec(str)
+  if (!matches) return false
+  const y: number = +matches[1]
+  const m: number = +matches[2]
+  const d: number = +matches[3]
+  return (
+    m >= 1 &&
+    m <= 12 &&
+    d >= 1 &&
+    (d <= DAYS[m] ||
+      // leap year: https://tools.ietf.org/html/rfc3339#appendix-C
+      (m === 2 && d === 29 && (y % 100 === 0 ? y % 400 === 0 : y % 4 === 0)))
+  )
+}
+
+function validTime(str: string): boolean {
+  const matches: string[] | null = TIME.exec(str)
+  if (!matches) return false
+  const hr: number = +matches[1]
+  const min: number = +matches[2]
+  const sec: number = +matches[3]
+  const tzH: number = +(matches[4] || 0)
+  const tzM: number = +(matches[5] || 0)
+  return (
+    (hr <= 23 && min <= 59 && sec <= 59) ||
+    // leap second
+    (hr - tzH === 23 && min - tzM === 59 && sec === 60)
+  )
+}
+
+validTimestamp.code = 'require("ajv/dist/runtime/timestamp").default'