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/object-keys/.eslintrc

@@ -0,0 +1,17 @@
+{
+	"root": true,
+
+	"extends": "@ljharb",
+
+	"rules": {
+		"complexity": [2, 23],
+		"id-length": [2, { "min": 1, "max": 40 }],
+		"max-params": [2, 3],
+		"max-statements": [2, 23],
+		"max-statements-per-line": [2, { "max": 2 }],
+		"no-extra-parens": [1],
+		"no-invalid-this": [1],
+		"no-restricted-syntax": [2, "BreakStatement", "ContinueStatement", "LabeledStatement", "WithStatement"],
+		"operator-linebreak": [2, "after"]
+	}
+}