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/postcss/lib/postcss.mjs

@@ -0,0 +1,30 @@
+import postcss from './postcss.js'
+
+export default postcss
+
+export const stringify = postcss.stringify
+export const fromJSON = postcss.fromJSON
+export const plugin = postcss.plugin
+export const parse = postcss.parse
+export const list = postcss.list
+
+export const document = postcss.document
+export const comment = postcss.comment
+export const atRule = postcss.atRule
+export const rule = postcss.rule
+export const decl = postcss.decl
+export const root = postcss.root
+
+export const CssSyntaxError = postcss.CssSyntaxError
+export const Declaration = postcss.Declaration
+export const Container = postcss.Container
+export const Processor = postcss.Processor
+export const Document = postcss.Document
+export const Comment = postcss.Comment
+export const Warning = postcss.Warning
+export const AtRule = postcss.AtRule
+export const Result = postcss.Result
+export const Input = postcss.Input
+export const Rule = postcss.Rule
+export const Root = postcss.Root
+export const Node = postcss.Node