Review: ODIN stale events and 0001-01-01 no-ETR sentinel (Refs #184)

ODIN still lists Avangrid rows from April 2026 (ETR April/May) as active on
2026-10-05; parse_odin now counts events whose own ETR passed >24h ago as
stale_customers_out, not customers_out, and since/etr come from live events.
Puget Sound Energy sends 0001-01-01T00:00:00Z for no ETR; treat as None.
Ack dialog now shows a refused enable's error instead of hiding it behind
the overlay.

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

drb-frontend/components/admin/OutageProvidersTab.tsx

@@ -40,6 +40,7 @@ export function OutageProvidersTab() {
 
   async function toggle(p: OutageProviderAdmin, enabled: boolean, acknowledge = false) {
     if (enabled && p.licence.gated && !acknowledge) {
+      setError(null);
       setAckChecked(false);
       setConfirming(p);
       return;
@@ -137,6 +138,7 @@ export function OutageProvidersTab() {
             <h2 id="outage-ack-title" className="text-white font-semibold">Enable {confirming.name}?</h2>
             <p className="text-red-300 text-sm font-semibold">{LICENCE_STYLE[confirming.licence.status].label}</p>
             <p className="text-gray-300 text-sm leading-snug">{confirming.licence.warning}</p>
+            {error && <p className="text-red-400 text-xs font-mono break-words">{error}</p>}
             <label className="flex items-start gap-2 text-sm text-gray-200">
               <input type="checkbox" checked={ackChecked} onChange={(e) => setAckChecked(e.target.checked)} className="mt-1" />
               <span>I confirm DRB holds the right to show this source&apos;s outage data. This confirmation is recorded with my account and the time in the audit log.</span>