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/refs/json-schema-2019-09/schema.json

@@ -0,0 +1,39 @@
+{
+  "$schema": "https://json-schema.org/draft/2019-09/schema",
+  "$id": "https://json-schema.org/draft/2019-09/schema",
+  "$vocabulary": {
+    "https://json-schema.org/draft/2019-09/vocab/core": true,
+    "https://json-schema.org/draft/2019-09/vocab/applicator": true,
+    "https://json-schema.org/draft/2019-09/vocab/validation": true,
+    "https://json-schema.org/draft/2019-09/vocab/meta-data": true,
+    "https://json-schema.org/draft/2019-09/vocab/format": false,
+    "https://json-schema.org/draft/2019-09/vocab/content": true
+  },
+  "$recursiveAnchor": true,
+
+  "title": "Core and Validation specifications meta-schema",
+  "allOf": [
+    {"$ref": "meta/core"},
+    {"$ref": "meta/applicator"},
+    {"$ref": "meta/validation"},
+    {"$ref": "meta/meta-data"},
+    {"$ref": "meta/format"},
+    {"$ref": "meta/content"}
+  ],
+  "type": ["object", "boolean"],
+  "properties": {
+    "definitions": {
+      "$comment": "While no longer an official keyword as it is replaced by $defs, this keyword is retained in the meta-schema to prevent incompatible extensions as it remains in common use.",
+      "type": "object",
+      "additionalProperties": {"$recursiveRef": "#"},
+      "default": {}
+    },
+    "dependencies": {
+      "$comment": "\"dependencies\" is no longer a keyword, but schema authors should avoid redefining it to facilitate a smooth transition to \"dependentSchemas\" and \"dependentRequired\"",
+      "type": "object",
+      "additionalProperties": {
+        "anyOf": [{"$recursiveRef": "#"}, {"$ref": "meta/validation#/$defs/stringArray"}]
+      }
+    }
+  }
+}