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-secure.json

@@ -0,0 +1,88 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://raw.githubusercontent.com/ajv-validator/ajv/master/lib/refs/json-schema-secure.json#",
+  "title": "Meta-schema for the security assessment of JSON Schemas",
+  "description": "If a JSON AnySchema fails validation against this meta-schema, it may be unsafe to validate untrusted data",
+  "definitions": {
+    "schemaArray": {
+      "type": "array",
+      "minItems": 1,
+      "items": {"$ref": "#"}
+    }
+  },
+  "dependencies": {
+    "patternProperties": {
+      "description": "prevent slow validation of large property names",
+      "required": ["propertyNames"],
+      "properties": {
+        "propertyNames": {
+          "required": ["maxLength"]
+        }
+      }
+    },
+    "uniqueItems": {
+      "description": "prevent slow validation of large non-scalar arrays",
+      "if": {
+        "properties": {
+          "uniqueItems": {"const": true},
+          "items": {
+            "properties": {
+              "type": {
+                "anyOf": [
+                  {
+                    "enum": ["object", "array"]
+                  },
+                  {
+                    "type": "array",
+                    "contains": {"enum": ["object", "array"]}
+                  }
+                ]
+              }
+            }
+          }
+        }
+      },
+      "then": {
+        "required": ["maxItems"]
+      }
+    },
+    "pattern": {
+      "description": "prevent slow pattern matching of large strings",
+      "required": ["maxLength"]
+    },
+    "format": {
+      "description": "prevent slow format validation of large strings",
+      "required": ["maxLength"]
+    }
+  },
+  "properties": {
+    "additionalItems": {"$ref": "#"},
+    "additionalProperties": {"$ref": "#"},
+    "dependencies": {
+      "additionalProperties": {
+        "anyOf": [{"type": "array"}, {"$ref": "#"}]
+      }
+    },
+    "items": {
+      "anyOf": [{"$ref": "#"}, {"$ref": "#/definitions/schemaArray"}]
+    },
+    "definitions": {
+      "additionalProperties": {"$ref": "#"}
+    },
+    "patternProperties": {
+      "additionalProperties": {"$ref": "#"}
+    },
+    "properties": {
+      "additionalProperties": {"$ref": "#"}
+    },
+    "if": {"$ref": "#"},
+    "then": {"$ref": "#"},
+    "else": {"$ref": "#"},
+    "allOf": {"$ref": "#/definitions/schemaArray"},
+    "anyOf": {"$ref": "#/definitions/schemaArray"},
+    "oneOf": {"$ref": "#/definitions/schemaArray"},
+    "not": {"$ref": "#"},
+    "contains": {"$ref": "#"},
+    "propertyNames": {"$ref": "#"}
+  }
+}