fix(frontend): add COOP/COEP headers for SharedArrayBuffer (wa-sqlite WASM)

Dev server now sends Cross-Origin-Opener-Policy and
Cross-Origin-Embedder-Policy headers required for WASM
SharedArrayBuffer support used by wa-sqlite.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/vite.config.js

@@ -42,6 +42,10 @@ export default defineConfig({
     }),
   ],
   server: {
+    headers: {
+      'Cross-Origin-Opener-Policy': 'same-origin',
+      'Cross-Origin-Embedder-Policy': 'require-corp',
+    },
     proxy: {
       '/api': {
         target: 'http://localhost:8000',