feat: Integrate GitHub Copilot SDK and LangChain for provider-independent orchestration

- Added @github/copilot-sdk and related dependencies for GitHub Copilot integration.
- Implemented ChatCopilot adapter for LangChain compatibility.
- Created LLM factory to return provider-specific models (OpenAI, Anthropic, Copilot).
- Developed Orchestrator agent using LangGraph for intent routing and context assembly.
- Enhanced IPC communication for streaming AI responses to the renderer.
- Updated progress documentation with implementation details and learnings.

src/preload/trpc.ts

@@ -18,3 +18,16 @@ contextBridge.exposeInMainWorld('electronTRPC', {
     };
   },
 });
+
+const AI_STREAM_CHANNEL = 'ai:stream';
+
+contextBridge.exposeInMainWorld('electronAI', {
+  /** Subscribe to AI streaming chunks. Returns an unsubscribe function. */
+  onStreamChunk: (cb: (data: { token: string; done: boolean }) => void) => {
+    const handler = (_event: Electron.IpcRendererEvent, data: { token: string; done: boolean }) => cb(data);
+    ipcRenderer.on(AI_STREAM_CHANNEL, handler);
+    return () => {
+      ipcRenderer.removeListener(AI_STREAM_CHANNEL, handler);
+    };
+  },
+});