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.d.mts

@@ -0,0 +1,69 @@
+export {
+  // Type-only exports
+  AcceptedPlugin,
+
+  AnyNode,
+  atRule,
+  AtRule,
+  AtRuleProps,
+  Builder,
+  ChildNode,
+  ChildProps,
+  comment,
+  Comment,
+  CommentProps,
+  Container,
+  ContainerProps,
+  CssSyntaxError,
+  decl,
+  Declaration,
+  DeclarationProps,
+  // postcss function / namespace
+  default,
+  document,
+  Document,
+  DocumentProps,
+  FilePosition,
+  fromJSON,
+  Helpers,
+  Input,
+
+  JSONHydrator,
+  // This is a class, but it’s not re-exported. That’s why it’s exported as type-only here.
+  type LazyResult,
+  list,
+  Message,
+  Node,
+  NodeErrorOptions,
+  NodeProps,
+  OldPlugin,
+  parse,
+  Parser,
+  // @ts-expect-error This value exists, but it’s untyped.
+  plugin,
+  Plugin,
+  PluginCreator,
+  Position,
+  Postcss,
+  ProcessOptions,
+  Processor,
+  Result,
+  root,
+  Root,
+  RootProps,
+  rule,
+  Rule,
+  RuleProps,
+  Source,
+  SourceMap,
+  SourceMapOptions,
+  Stringifier,
+  // Value exports from postcss.mjs
+  stringify,
+  Syntax,
+  TransformCallback,
+  Transformer,
+  Warning,
+
+  WarningOptions
+} from './postcss.js'