feat: output channel redesign - per-channel output gates, LLM chain events, SDKConfig

- Output channels generate per-channel tools: output_send__{name} (type=output) + output_send__{name}_help
- content is JSON string transparently passed to plugin handler for routing
- EventAgentLLMChain: full LLM response forwarded after each turn for webui/logs
- sdk.New refactored to SDKConfig struct (no more 13 positional args)
- RegisterOutputChannel adds desc param for JSON format documentation
- channelDevice simplified (no Tools method), desc field added
- Child agent permission updated for output_send__ prefix
- System prompt: output gates, multi-call, long messages split
- WebUI: subscribes to EventAgentLLMChain in SSE, no output channel
- Tests updated for new naming convention

internal/plugins/agentcli/plugin_test.go

@@ -31,8 +31,7 @@ func (tc *toolCapture) RegisterAPI(name string) error                          {
 func setupPlugin() (*Plugin, *toolCapture, error) {
 	p := New("agentcli")
 	tc := newToolCapture()
-	// Use nil for fields we don't need (iom, eventBus, etc.)
-	sdk := sdk.New("agentcli", nil, nil, nil, nil, nil, nil, nil, nil, tc.RegisterTool, tc.RegisterStage, tc.RegisterAPI)
+	sdk := sdk.New("agentcli", sdk.SDKConfig{RegTool: tc.RegisterTool, RegStage: tc.RegisterStage, RegAPI: tc.RegisterAPI})
 	if err := p.Start(sdk); err != nil {
 		return nil, nil, err
 	}