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/stackback/index.js

@@ -0,0 +1,46 @@
+
+// v8 builtin format stack trace
+// for when there was no previous prepareStackTrace function to call
+var FormatStackTrace = require('./formatstack');
+
+// some notes on the behavior below:
+// because the 'stack' member is a one shot access variable (the raw stack is
+// formatted on accessing it)
+// we try to avoid modifying what the user would have wanted
+// thus we use the previous value for prepareStackTrace
+//
+// The reason we store the callsite variable is because prepareStackTrace
+// will not be called again once it has been called for a given error object
+// but we want to support getting the stack out of the error multiple times (cause why not)
+module.exports = function(err) {
+
+    // save original stacktrace
+    var save = Error.prepareStackTrace;
+
+    // replace capture with our function
+    Error.prepareStackTrace =  function(err, trace) {
+
+        // cache stack frames so we don't have to get them again
+        // use a non-enumerable property
+        Object.defineProperty(err, '_sb_callsites', {
+            value: trace
+        });
+
+        return (save || FormatStackTrace)(err, trace);
+    };
+
+    // force capture of the stack frames
+    err.stack;
+
+    // someone already asked for the stack so we can't do this trick
+    // TODO fallback to string parsing?
+    if (!err._sb_callsites) {
+        return [];
+    }
+
+    // return original capture function
+    Error.prepareStackTrace = save;
+
+    return err._sb_callsites;
+};
+