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/plugin/bridge_e2e_test.go

@@ -42,7 +42,7 @@ func TestBridgeE2E_WebPlugin(t *testing.T) {
 	}
 
 	sett := sdk.NewSettings("web", nil)
-	psdk := sdk.New("web", nil, nil, nil, nil, nil, nil, nil, sett, regTool, regStage, regAPI)
+	psdk := sdk.New("web", sdk.SDKConfig{Settings: sett, RegTool: regTool, RegStage: regStage, RegAPI: regAPI})
 
 	plg, err := newDLLPlugin(dllPath, "web", nil)
 	if err != nil {
@@ -136,11 +136,11 @@ func TestBridgeE2E_SanitizerStages(t *testing.T) {
 	}
 
 	sett := sdk.NewSettings("sanitizer", nil)
-	psdk := sdk.New("sanitizer", nil, nil, nil, nil, nil, nil, nil, sett,
-		func(name string, def sdk.ToolDef, handler sdk.ToolHandler) error { return nil },
-		regStage,
-		func(name string) error { return nil },
-	)
+	psdk := sdk.New("sanitizer", sdk.SDKConfig{Settings: sett,
+		RegTool: func(name string, def sdk.ToolDef, handler sdk.ToolHandler) error { return nil },
+		RegStage: regStage,
+		RegAPI:   func(name string) error { return nil },
+	})
 
 	plg, err := newDLLPlugin(dllPath, "sanitizer", nil)
 	if err != nil {