Drop redundant Platform row from agent SystemInfoCard

The agent-variant card showed Platform and OS as separate rows. For
hosts where osName already carries the platform identity (Proxmox VE,
Unraid, TrueNAS), the Platform row repeated the broader OS family
("debian", "raspbian", "linux") next to the more specific osName,
implying that "debian" was the platform when the host is actually
Proxmox VE.

Merge the Platform row into the OS row. When osName is present it
carries the full identity; when it is missing the OS row falls back
to the prettified platform family. Architecture and Kernel stay on
their own rows.

Mirrors the connection-table identity fix in 1b2ac272c so both the
Settings/Infrastructure surface and the resource detail drawer agree
on the canonical platform identity.

frontend-modern/src/components/shared/cards/SystemInfoCard.tsx

@@ -58,19 +58,19 @@ export const SystemInfoCard: Component<SystemInfoCardProps> = (props) => {
             {agentInfo.hostname}
           </span>
         </div>
-        <div class="flex items-center justify-between">
-          <span class="text-muted">Platform</span>
-          <span class="font-medium text-base-content capitalize">
-            {agentInfo.platform || 'Unknown'}
-          </span>
-        </div>
         <div class="flex items-center justify-between gap-2 min-w-0">
           <span class="text-muted shrink-0">OS</span>
           <span
             class="font-medium text-base-content truncate"
-            title={`${agentInfo.osName} ${agentInfo.osVersion}`}
+            title={
+              agentInfo.osName
+                ? `${agentInfo.osName}${agentInfo.osVersion ? ` ${agentInfo.osVersion}` : ''}`
+                : agentInfo.platform || 'Unknown'
+            }
           >
-            {agentInfo.osName} {agentInfo.osVersion}
+            {agentInfo.osName
+              ? `${agentInfo.osName}${agentInfo.osVersion ? ` ${agentInfo.osVersion}` : ''}`
+              : agentInfo.platform || 'Unknown'}
           </span>
         </div>
         <div class="flex items-center justify-between gap-2 min-w-0">