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/stringifier.d.ts

@@ -0,0 +1,46 @@
+import {
+  AnyNode,
+  AtRule,
+  Builder,
+  Comment,
+  Container,
+  Declaration,
+  Document,
+  Root,
+  Rule
+} from './postcss.js'
+
+declare namespace Stringifier {
+   
+  export { Stringifier_ as default }
+}
+
+declare class Stringifier_ {
+  builder: Builder
+  constructor(builder: Builder)
+  atrule(node: AtRule, semicolon?: boolean): void
+  beforeAfter(node: AnyNode, detect: 'after' | 'before'): string
+  block(node: AnyNode, start: string): void
+  body(node: Container): void
+  comment(node: Comment): void
+  decl(node: Declaration, semicolon?: boolean): void
+  document(node: Document): void
+  raw(node: AnyNode, own: null | string, detect?: string): boolean | string
+  rawBeforeClose(root: Root): string | undefined
+  rawBeforeComment(root: Root, node: Comment): string | undefined
+  rawBeforeDecl(root: Root, node: Declaration): string | undefined
+  rawBeforeOpen(root: Root): string | undefined
+  rawBeforeRule(root: Root): string | undefined
+  rawColon(root: Root): string | undefined
+  rawEmptyBody(root: Root): string | undefined
+  rawIndent(root: Root): string | undefined
+  rawSemicolon(root: Root): boolean | undefined
+  rawValue(node: AnyNode, prop: string): number | string
+  root(node: Root): void
+  rule(node: Rule): void
+  stringify(node: AnyNode, semicolon?: boolean): void
+}
+
+declare class Stringifier extends Stringifier_ {}
+
+export = Stringifier