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

gui/preload.js

@@ -0,0 +1,11 @@
+const { contextBridge, ipcRenderer } = require('electron');
+
+contextBridge.exposeInMainWorld('homeagent', {
+  connections: {
+    list: () => ipcRenderer.invoke('connections:list'),
+    add: (conn) => ipcRenderer.invoke('connections:add', conn),
+    update: (id, updates) => ipcRenderer.invoke('connections:update', { id, updates }),
+    delete: (id) => ipcRenderer.invoke('connections:delete', id),
+    setCurrent: (id) => ipcRenderer.invoke('connections:setCurrent', id),
+  },
+});