Log official NWS observations for a reference ZIP and overlay them on the dashboard

- Resolves ZIP (default 24550) to the nearest NWS observation station; logs every observation
  (normalised imperial values + raw METAR), back-fills ~7 days, snapshots the hourly forecast
  every 3h, and logs alerts for that point
- Chart overlay (temp, humidity/dew point, wind, pressure) with an NWS toggle in the History bar
- 'Official NWS observation' card on the Now tab comparing against your station
- Settings: change the reference ZIP and see logging status
- Exact-unit conversions for NWS values (verified against known conversions)

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

app/public/dashboard-ui.css

@@ -145,3 +145,9 @@ a { color: var(--ui); }
 .ah-desc { white-space: pre-wrap; }
 .ah-meaning { padding: 0.5rem 0.7rem; border-radius: 10px; background: color-mix(in srgb, var(--ui) 10%, transparent); }
 .ah-note { font-size: 0.74rem; color: var(--ink-light); }
+
+/* NWS overlay + card */
+.nws-toggle.active { background: #7c5cff !important; border-color: #7c5cff !important; }
+.nws-dot { display: inline-block; width: 8px; height: 8px; border-radius: 50%; background: #a78bfa; margin-left: 0.35rem; vertical-align: middle; }
+.nws-card .kv b { font-size: 1.05rem; }
+.nws-raw { display: block; margin-top: 0.4rem; font-size: 0.7rem; overflow-wrap: anywhere; color: var(--ink-light); background: var(--paper); border: 1px solid var(--border); border-radius: 8px; padding: 0.35rem 0.55rem; }