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/vocabularies/jtd/metadata.ts

@@ -0,0 +1,24 @@
+import {KeywordCxt} from "../../ajv"
+import type {CodeKeywordDefinition} from "../../types"
+import {alwaysValidSchema} from "../../compile/util"
+
+const def: CodeKeywordDefinition = {
+  keyword: "metadata",
+  schemaType: "object",
+  code(cxt: KeywordCxt) {
+    checkMetadata(cxt)
+    const {gen, schema, it} = cxt
+    if (alwaysValidSchema(it, schema)) return
+    const valid = gen.name("valid")
+    cxt.subschema({keyword: "metadata", jtdMetadata: true}, valid)
+    cxt.ok(valid)
+  },
+}
+
+export function checkMetadata({it, keyword}: KeywordCxt, metadata?: boolean): void {
+  if (it.jtdMetadata !== metadata) {
+    throw new Error(`JTD: "${keyword}" cannot be used in this schema location`)
+  }
+}
+
+export default def