Support list file input for `CF_EXCLUDE_MODS` and `CF_INCLUDE_MODS`

### Enhancement Type

Improve an existing feature

### Describe the enhancement

It would be useful if `CF_EXCLUDE_MODS` and `CF_INCLUDE_MODS` could support the `@file` syntax, similar to how `CURSEFORGE_FILES: "@/extras/cf-mods.txt"` works.

This would help with managing longer mod include/exclude lists in a cleaner and more maintainable way, especially in shared or version-controlled environments.

Start by locating the entry point that processes CF_EXCLUDE_MODS and CF_INCLUDE_MODS, then compare its handling with the existing CURSEFORGE_FILES @file syntax. Verify the behavior with longer include and exclude lists stored in files, including the existing CURSEFORGE_FILES pattern.

Written by the indexing model from the issue text.