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/dist/refs/json-schema-2020-12/schema.json

@@ -0,0 +1,55 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://json-schema.org/draft/2020-12/schema",
+  "$vocabulary": {
+    "https://json-schema.org/draft/2020-12/vocab/core": true,
+    "https://json-schema.org/draft/2020-12/vocab/applicator": true,
+    "https://json-schema.org/draft/2020-12/vocab/unevaluated": true,
+    "https://json-schema.org/draft/2020-12/vocab/validation": true,
+    "https://json-schema.org/draft/2020-12/vocab/meta-data": true,
+    "https://json-schema.org/draft/2020-12/vocab/format-annotation": true,
+    "https://json-schema.org/draft/2020-12/vocab/content": true
+  },
+  "$dynamicAnchor": "meta",
+
+  "title": "Core and Validation specifications meta-schema",
+  "allOf": [
+    {"$ref": "meta/core"},
+    {"$ref": "meta/applicator"},
+    {"$ref": "meta/unevaluated"},
+    {"$ref": "meta/validation"},
+    {"$ref": "meta/meta-data"},
+    {"$ref": "meta/format-annotation"},
+    {"$ref": "meta/content"}
+  ],
+  "type": ["object", "boolean"],
+  "$comment": "This meta-schema also defines keywords that have appeared in previous drafts in order to prevent incompatible extensions as they remain in common use.",
+  "properties": {
+    "definitions": {
+      "$comment": "\"definitions\" has been replaced by \"$defs\".",
+      "type": "object",
+      "additionalProperties": {"$dynamicRef": "#meta"},
+      "deprecated": true,
+      "default": {}
+    },
+    "dependencies": {
+      "$comment": "\"dependencies\" has been split and replaced by \"dependentSchemas\" and \"dependentRequired\" in order to serve their differing semantics.",
+      "type": "object",
+      "additionalProperties": {
+        "anyOf": [{"$dynamicRef": "#meta"}, {"$ref": "meta/validation#/$defs/stringArray"}]
+      },
+      "deprecated": true,
+      "default": {}
+    },
+    "$recursiveAnchor": {
+      "$comment": "\"$recursiveAnchor\" has been replaced by \"$dynamicAnchor\".",
+      "$ref": "meta/core#/$defs/anchorString",
+      "deprecated": true
+    },
+    "$recursiveRef": {
+      "$comment": "\"$recursiveRef\" has been replaced by \"$dynamicRef\".",
+      "$ref": "meta/core#/$defs/uriReferenceString",
+      "deprecated": true
+    }
+  }
+}