feat: integrate vectordb for note embeddings

- Added `vectordb` as a dependency in `package.json`.
- Implemented `embedText` function in `src/main/ai/embeddings.ts` to handle text embeddings using GitHub Copilot OAuth token or OpenAI token.
- Created `vectordb.ts` for managing LanceDB connection and embedding notes with upsert strategy.
- Updated `index.ts` to initialize vector database and migrate existing notes on app ready.
- Modified `router/index.ts` to fire-and-forget embedding calls on note creation and updates.
- Enhanced `progress.txt` with detailed implementation notes and learnings regarding the integration.

src/main/index.ts

@@ -5,6 +5,7 @@ import { initDb } from './db';
 import { appRouter } from './router';
 import { createIPCHandler } from './ipc';
 import { initAI } from './ai/provider';
+import { initVectorDb, migrateNotesIfNeeded } from './db/vectordb';
 // Import to trigger provider registration before initAI() runs
 import './ai/copilot';
 
@@ -54,6 +55,10 @@ app.on('ready', () => {
   createIPCHandler({ router: appRouter, windows: [win] });
   // AI init is best-effort — never block window creation
   initAI().catch((err) => console.error('[AI] Init failed:', err));
+  // Vector DB init + migration is best-effort — runs after window is shown
+  initVectorDb()
+    .then(() => migrateNotesIfNeeded())
+    .catch((err) => console.error('[VectorDB] Init or migration failed:', err));
 });
 
 // Quit when all windows are closed, except on macOS. There, it's common