fix(scan): show validator "Registered" timestamp on detail page

Operator noticed the validators page has no "how long has this validator
been online" indicator. The chain's legacy /validators endpoint exposes
`registered_at` (unix seconds) but the merge in fetchValidators only pulled
name + blocks_produced from it. Now carries `registered_at` through to the
merged row and renders a "Registered" InfoRow on the detail page under
Status.

List page stays clean — detail-page surface is the standard explorer
pattern (Etherscan's "Created" / Solana Beach's "Started" both live on
the detail page, not the list).

Field already existed on ValidatorData; no chain-side change needed.

Author: satyakwok

apps/scan/app/[locale]/validators/[address]/page.tsx

@@ -186,6 +186,9 @@ export default function ValidatorDetailPage({ params }: { params: Promise<{ addr
               <InfoRow label="Name" value={validator.name ?? "-"} />
               <InfoRow label="Address" value={<Address address={validator.address} truncate={false} />} />
               <InfoRow label="Status" value={<span className={`inline-flex items-center gap-1.5 text-sm ${st.color}`}>{st.icon}{st.text}</span>} />
+              {validator.registered_at !== undefined && validator.registered_at > 0 && (
+                <InfoRow label="Registered" value={<Timestamp timestamp={validator.registered_at} />} />
+              )}
               {validator.stake !== undefined && (
                 <InfoRow label="Stake" value={<span className="font-mono">{formatNumber(validator.stake)} SRX</span>} />
               )}

apps/scan/lib/api.ts

@@ -553,6 +553,9 @@ export async function fetchValidators(network: NetworkId) {
     return {
       ...v,
       name: v.name ?? legacy?.name ?? "",
+      // `registered_at` (unix seconds) is on /validators but not /staking/validators.
+      // Carry it across so the detail page can show "online since <date>".
+      registered_at: v.registered_at ?? legacy?.registered_at,
       // Prefer the larger of the two block counters. /staking/validators
       // tracks blocks_signed which can reset on chain restart; legacy
       // /validators carries the cumulative blocks_produced. Take whichever