feat(M35): dynamic target configuration with encrypted config, test connection, and GUI updates

Mirror M34's dynamic issuer config pattern for deployment targets: AES-256-GCM
encrypted config storage, sensitive field redaction in API responses, agent
heartbeat-based test connection endpoint, and full frontend updates including
test status indicators, source badges, and removal of stale hostname/status
fields from the Target interface.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/pages/CertificateDetailPage.tsx

@@ -660,7 +660,7 @@ export default function CertificateDetailPage() {
             >
               <option value="">Choose a target...</option>
               {targets?.data?.map(t => (
-                <option key={t.id} value={t.id}>{t.name} ({t.type} — {t.hostname})</option>
+                <option key={t.id} value={t.id}>{t.name} ({t.type})</option>
               ))}
             </select>
             <div className="flex justify-end gap-3">