[Bug]: Hidden directories (starting with ".") are ignored when building in bundleless mode

[Karibash]

Version

System:
    OS: macOS 15.6.1
    CPU: (11) arm64 Apple M3 Pro
    Memory: 90.36 MB / 36.00 GB
    Shell: 4.0.2 - /opt/homebrew/bin/fish
  Browsers:
    Chrome: 139.0.7258.140
    Safari: 18.6
  npmPackages:
    @rslib/core: 0.12.3 => 0.12.3

Details

When building in bundleless mode, directories whose names start with a dot (.) are ignored.
This causes files inside such directories not to be included in the build output.

Expected behavior

Hidden directories (e.g., .generated) should be processed the same way as normal directories, unless explicitly excluded by configuration.

Reproduce link

https://codesandbox.io/p/devbox/aged-currying-forked-xpkdq4?workspaceId=ws_4RzLomoT7g4GnfzMUfgpRN

Reproduce Steps

1. Run the build process.