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/renderer/lib/ipcLink.ts

@@ -13,9 +13,14 @@ interface ElectronTRPC {
   onMessage: (cb: (data: unknown) => void) => (() => void) | void;
 }
 
+interface ElectronAI {
+  onStreamChunk: (cb: (data: { token: string; done: boolean }) => void) => () => void;
+}
+
 declare global {
   interface Window {
     electronTRPC: ElectronTRPC;
+    electronAI: ElectronAI;
   }
 }