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/jsonpointer/jsonpointer.js

@@ -0,0 +1,100 @@
+var hasExcape = /~/
+var escapeMatcher = /~[01]/g
+function escapeReplacer (m) {
+  switch (m) {
+    case '~1': return '/'
+    case '~0': return '~'
+  }
+  throw new Error('Invalid tilde escape: ' + m)
+}
+
+function untilde (str) {
+  if (!hasExcape.test(str)) return str
+  return str.replace(escapeMatcher, escapeReplacer)
+}
+
+function setter (obj, pointer, value) {
+  var part
+  var hasNextPart
+
+  for (var p = 1, len = pointer.length; p < len;) {
+    if (pointer[p] === 'constructor' || pointer[p] === 'prototype' || pointer[p] === '__proto__') return obj
+
+    part = untilde(pointer[p++])
+    hasNextPart = len > p
+
+    if (typeof obj[part] === 'undefined') {
+      // support setting of /-
+      if (Array.isArray(obj) && part === '-') {
+        part = obj.length
+      }
+
+      // support nested objects/array when setting values
+      if (hasNextPart) {
+        if ((pointer[p] !== '' && pointer[p] < Infinity) || pointer[p] === '-') obj[part] = []
+        else obj[part] = {}
+      }
+    }
+
+    if (!hasNextPart) break
+    obj = obj[part]
+  }
+
+  var oldValue = obj[part]
+  if (value === undefined) delete obj[part]
+  else obj[part] = value
+  return oldValue
+}
+
+function compilePointer (pointer) {
+  if (typeof pointer === 'string') {
+    pointer = pointer.split('/')
+    if (pointer[0] === '') return pointer
+    throw new Error('Invalid JSON pointer.')
+  } else if (Array.isArray(pointer)) {
+    for (const part of pointer) {
+      if (typeof part !== 'string' && typeof part !== 'number') {
+        throw new Error('Invalid JSON pointer. Must be of type string or number.')
+      }
+    }
+    return pointer
+  }
+
+  throw new Error('Invalid JSON pointer.')
+}
+
+function get (obj, pointer) {
+  if (typeof obj !== 'object') throw new Error('Invalid input object.')
+  pointer = compilePointer(pointer)
+  var len = pointer.length
+  if (len === 1) return obj
+
+  for (var p = 1; p < len;) {
+    obj = obj[untilde(pointer[p++])]
+    if (len === p) return obj
+    if (typeof obj !== 'object' || obj === null) return undefined
+  }
+}
+
+function set (obj, pointer, value) {
+  if (typeof obj !== 'object') throw new Error('Invalid input object.')
+  pointer = compilePointer(pointer)
+  if (pointer.length === 0) throw new Error('Invalid JSON pointer for set.')
+  return setter(obj, pointer, value)
+}
+
+function compile (pointer) {
+  var compiled = compilePointer(pointer)
+  return {
+    get: function (object) {
+      return get(object, compiled)
+    },
+    set: function (object, value) {
+      return set(object, compiled, value)
+    }
+  }
+}
+
+exports.get = get
+exports.set = set
+exports.compile = compile