fix: copy better-sqlite3 native bindings to Docker runtime stage

The .node binary wasn't being copied to .output, causing 'Could not locate
the bindings file' error at runtime.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nuxt.config.ts

@@ -10,5 +10,8 @@ export default defineNuxtConfig({
 
   nitro: {
     experimental: { tasks: true },
+    externals: {
+      external: ['better-sqlite3'],
+    },
   },
 })