Persistent station records, backups, and iPhone-friendly dashboard

- Keep per-day extremes in data/records.json (merge-only) and derive all-time,
  notable-day, monthly and yearly records from it; rebuild from raw files at startup
- Use station maxdailygust for true gust extremes
- Add /api/station/backup.jsonl, records-backup.json and records/rebuild
- Dashboard: safe-area insets, 44px touch targets, scrollable nav/range bars,
  chart touch-action, standalone PWA manifest + apple meta tags

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

app/public/dashboard.webmanifest

@@ -0,0 +1,16 @@
+{
+  "name": "Station Dashboard",
+  "short_name": "Station",
+  "description": "Personal weather station dashboard",
+  "start_url": "/dashboard",
+  "scope": "/dashboard",
+  "display": "standalone",
+  "background_color": "#191510",
+  "theme_color": "#191510",
+  "orientation": "any",
+  "categories": ["weather", "utilities"],
+  "icons": [
+    { "src": "/icons/icon-192.png", "sizes": "192x192", "type": "image/png", "purpose": "any" },
+    { "src": "/icons/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable" }
+  ]
+}