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/signal-exit/dist/cjs/signals.d.ts

@@ -0,0 +1,29 @@
+/// <reference types="node" />
+/**
+ * This is not the set of all possible signals.
+ *
+ * It IS, however, the set of all signals that trigger
+ * an exit on either Linux or BSD systems.  Linux is a
+ * superset of the signal names supported on BSD, and
+ * the unknown signals just fail to register, so we can
+ * catch that easily enough.
+ *
+ * Windows signals are a different set, since there are
+ * signals that terminate Windows processes, but don't
+ * terminate (or don't even exist) on Posix systems.
+ *
+ * Don't bother with SIGKILL.  It's uncatchable, which
+ * means that we can't fire any callbacks anyway.
+ *
+ * If a user does happen to register a handler on a non-
+ * fatal signal like SIGWINCH or something, and then
+ * exit, it'll end up firing `process.emit('exit')`, so
+ * the handler will be fired anyway.
+ *
+ * SIGBUS, SIGFPE, SIGSEGV and SIGILL, when not raised
+ * artificially, inherently leave the process in a
+ * state from which it is not safe to try and enter JS
+ * listeners.
+ */
+export declare const signals: NodeJS.Signals[];
+//# sourceMappingURL=signals.d.ts.map