Alert history: say what each alert is for, where, and when

- Plain-language meaning for common NWS products, shown in the row and expanded view
- Details column: reason, area, severity, effective window; click for full text/instructions
- New alerts log area, severity, urgency, certainty and sender
- Older entries are filled in from NWS by alert id (cached in data/alert-details.json);
  alerts NWS no longer serves fall back to the built-in meaning

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

app/public/dashboard-ui.css

@@ -131,3 +131,17 @@ a { color: var(--ui); }
 .rec-yr { display: block; font-size: 0.68rem; color: var(--ink-light); font-weight: 600; white-space: nowrap; }
 
 .rec-cal tr.empty { opacity: .4; }
+
+/* Alert history: what / where / when */
+.ah-what { font-size: 0.86rem; line-height: 1.4; }
+.ah-meta { margin-top: 0.25rem; font-size: 0.74rem; color: var(--ink-light); line-height: 1.5; }
+.ah-sev { display: inline-block; padding: 0 0.45rem; border-radius: 99px; font-weight: 700; font-size: 0.68rem; border: 1px solid var(--border); }
+.ah-sev.sev-extreme { color: #ef4444; border-color: #ef4444; } .ah-sev.sev-severe { color: #f97316; border-color: #f97316; }
+.ah-sev.sev-moderate { color: #eab308; border-color: #eab308; } .ah-sev.sev-minor { color: var(--cool); border-color: var(--cool); }
+.ah-row { cursor: pointer; }
+.ah-row.open td { background: color-mix(in srgb, var(--ui) 6%, transparent); }
+.ah-full { margin-top: 0.6rem; padding-top: 0.6rem; border-top: 1px dashed var(--border); font-size: 0.82rem; line-height: 1.5; cursor: default; }
+.ah-full p { margin: 0 0 0.5rem; }
+.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); }