Alerts tab: fix hurricane/tropical storm bugs; rich alert cards matching the dashboard

Hurricane / tropical storm fixes
- NHC intensity is in knots: show real mph (80 kt = 92 mph) instead of mislabelled 'mph'
- Real Saffir-Simpson category from wind (was always cat 1); subtropical, post-tropical and
  potential-cyclone types no longer shown as 'depression'; each storm shows movement
  (direction + mph, previously a non-existent field), distance from you, update time, advisory link
- Forecast track points coloured by their own forecast strength (not the current class)
- Map click handlers registered once (popups stacked on every refresh); overlays wait for the
  map to settle instead of silently not drawing while tiles load; stale renders superseded
- Subtropical/tropical advice added to alert guidance; escaped storm names

Alert cards (active alerts only)
- What it's for, area, window, time remaining, plain-language meaning, what to do, and a
  Full details expander (headline, text, instructions, severity/urgency/certainty, issuer)
- No longer drops alerts beyond 6 per severity group; expired alerts are filtered out
- Shared plain-language alert glossary (alert-info.js, 64 products incl. tropical and surge)
  now used by both the app and the dashboard history

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/public/sw.js

@@ -4,7 +4,7 @@ self.addEventListener('message', event => {
   if (event.data === 'skipWaiting') self.skipWaiting();
 });
 
-const CACHE = 'weather-v11';
+const CACHE = 'weather-v12';
 
 // App shell cached on install for offline resilience.
 const PRECACHE = [
@@ -15,6 +15,7 @@ const PRECACHE = [
   '/station-live.js',
   '/app-ui.css',
   '/pwa-safe.css',
+  '/alert-info.js',
   '/app-ui.js',
   '/manifest.json',
   '/icons/icon.svg'