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

backend/app/api/v1/router.py

@@ -589,6 +589,16 @@ def traffic_flow_key(node_id: str, raw_flow: dict[str, object]) -> tuple[object,
     )
 
 
+def compact_agent_payload(payload: AgentHeartbeat) -> dict:
+    value = payload.model_dump(mode="json")
+    flows = value.get("flows")
+    if isinstance(flows, list):
+        value["flow_count"] = len(flows)
+        value["flows"] = flows[:50]
+        value["flows_truncated"] = len(flows) > 50
+    return value
+
+
 def policy_read_payload(policy: Policy, deployment_status: dict[str, object] | None = None) -> dict[str, object]:
     return {
         "id": policy.id,
@@ -1336,7 +1346,7 @@ cat > "$CONFIG_DIR/config.json" <<'JSON'
   "node_id": "{node.id}",
   "node_name": "{node.name}",
   "interval_seconds": 30,
-  "flow_limit": 2000,
+  "flow_limit": 1500,
   "packet_flow_collector": true,
   "packet_flow_window_seconds": 10,
   "firewall_log_collector": true,
@@ -1454,7 +1464,7 @@ def agent_heartbeat(payload: AgentHeartbeat, authorization: str | None = Header(
     agent.status = "online"
     agent.version = payload.version
     agent.last_seen_at = datetime.utcnow()
-    agent.last_payload = payload.model_dump(mode="json")
+    agent.last_payload = compact_agent_payload(payload)
     retention_hours = runtime_settings_payload(db).flow_retention_hours
     retention_cutoff = datetime.utcnow() - timedelta(hours=retention_hours)
     for old_flow in db.scalars(select(TrafficFlow).where(TrafficFlow.node_id == node.id, TrafficFlow.updated_at < retention_cutoff)).all():