Get Observability Agents

Agent activity rollup over the selected window (default last 24h).

One row per Streamkap agent (joined with MongoDB agents for the friendly name) plus one per (project_key_id, client_id) external pseudo-agent. Streamkap counts combine MCP-server calls (streamkap_mcp_log) with agent-runtime trace activity (agent_traces), so an agent that only processes records still surfaces a real count. The FE passes its selected range so the sidebar matches the active view. Sorted newest-active-first.