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/sourcemap-codec/README.md

@@ -0,0 +1,63 @@
+# sourcemap-codec
+
+Encode/decode the `mappings` property of a [sourcemap](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit).
+
+
+## Why?
+
+Sourcemaps are difficult to generate and manipulate, because the `mappings` property – the part that actually links the generated code back to the original source – is encoded using an obscure method called [Variable-length quantity](https://en.wikipedia.org/wiki/Variable-length_quantity). On top of that, each segment in the mapping contains offsets rather than absolute indices, which means that you can't look at a segment in isolation – you have to understand the whole sourcemap.
+
+This package makes the process slightly easier.
+
+
+## Installation
+
+```bash
+npm install sourcemap-codec
+```
+
+
+## Usage
+
+```js
+import { encode, decode } from 'sourcemap-codec';
+
+var decoded = decode( ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );
+
+assert.deepEqual( decoded, [
+	// the first line (of the generated code) has no mappings,
+	// as shown by the starting semi-colon (which separates lines)
+	[],
+
+	// the second line contains four (comma-separated) segments
+	[
+		// segments are encoded as you'd expect:
+		// [ generatedCodeColumn, sourceIndex, sourceCodeLine, sourceCodeColumn, nameIndex ]
+
+		// i.e. the first segment begins at column 2, and maps back to the second column
+		// of the second line (both zero-based) of the 0th source, and uses the 0th
+		// name in the `map.names` array
+		[ 2, 0, 2, 2, 0 ],
+
+		// the remaining segments are 4-length rather than 5-length,
+		// because they don't map a name
+		[ 4, 0, 2, 4 ],
+		[ 6, 0, 2, 5 ],
+		[ 7, 0, 2, 7 ]
+	],
+
+	// the final line contains two segments
+	[
+		[ 2, 1, 10, 19 ],
+		[ 12, 1, 11, 20 ]
+	]
+]);
+
+var encoded = encode( decoded );
+assert.equal( encoded, ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );
+```
+
+
+# License
+
+MIT