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.

vite.main.config.mts

@@ -5,7 +5,19 @@ export default defineConfig({
   build: {
     rollupOptions: {
       // Externalize native Node modules — they're rebuilt by electron-forge
-      external: ['better-sqlite3', 'keytar'],
+      external: [
+        'better-sqlite3',
+        'keytar',
+        '@github/copilot-sdk',
+        '@github/copilot',
+        // LangChain — externalize to avoid bundling Node.js-specific code
+        '@langchain/core',
+        '@langchain/langgraph',
+        '@langchain/openai',
+        '@langchain/anthropic',
+        '@langchain/langgraph-checkpoint',
+        '@langchain/langgraph-sdk',
+      ],
       output: {
         entryFileNames: 'main.js',
       },