feat(vue-server): server/client convention

[hi-ogawa]

• define server / client (tentative)
  • client if "use client" or non .server.vue
    • for .vue file, we need to switch two vue plugins early. we could switch two mode inside our own plugin by checking file content, but we don't do that yet.
  • otherwise server
  • TODO: what about external? (local re-export to workaround)
• detect boundary
  • by definition, client boundary is where "server" imports "client"
• build
  • multi pass build (scan to detect boundary before main build?)

todo

• dev
• build