feat: reduce agent payload size with flow truncation and increase nginx body size limit to 16MB

Reduce agent flow_limit from 2000 to 1500, truncate log_excerpt from 500 to 180 characters in firewall log parsing, increase firewall_log_lines_from_files limit from default to max(limit*2, 1000), add compact_agent_payload to truncate flows array to 50 entries with flow_count/flows_truncated metadata, update agent_heartbeat to store compacted payload instead of full dump, add agentFlowCount helper to

frontend/src/pages/Nodes.tsx

@@ -47,6 +47,14 @@ export function Nodes() {
     return Array.isArray(interfaceTraffic) ? interfaceTraffic : [];
   }
 
+  function agentFlowCount(node: Node) {
+    const count = node.agent?.last_payload?.flow_count;
+    if (typeof count === "number") {
+      return count;
+    }
+    return agentFlows(node).length;
+  }
+
   function agentInterfaces(node: Node) {
     const interfaces = node.agent?.last_payload?.interfaces;
     return Array.isArray(interfaces) ? interfaces : [];
@@ -158,7 +166,7 @@ export function Nodes() {
               </div>
               <div className="rounded-md border border-border bg-canvas p-3">
                 <div className="text-xs text-slate-500 dark:text-slate-400">Flows</div>
-                <div className="mt-1 text-sm font-medium">{agentFlows(detailNode).length}</div>
+                <div className="mt-1 text-sm font-medium">{agentFlowCount(detailNode)}</div>
               </div>
               <div className="rounded-md border border-border bg-canvas p-3">
                 <div className="text-xs text-slate-500 dark:text-slate-400">Conntrack</div>