[fullstack] inconsistent server css collection between dev and build

[hi-ogawa]

• dev: mod?.importedModules
  • this collects dynamic imports

https://github.com/hi-ogawa/vite-plugins/blob/fc13aec76014c1f9bbf94138e2f7b9e9e4d5dcda/packages/fullstack/src/plugin.ts#L565-L596

• build: v.imports
  • this doesn't collect dynamic imports

https://github.com/hi-ogawa/vite-plugins/blob/fc13aec76014c1f9bbf94138e2f7b9e9e4d5dcda/packages/fullstack/src/plugin.ts#L672-L686