New filehighlight.rs module categorizes files by extension into 9 types
(Normal, Executable, Archive, Audio, Video, Image, Source, Documentation,
Database). Each type maps to a theme palette color via file_type_color().
entry_style() in mod.rs now applies file type colors for non-directory,
non-symlink files. Executable detection uses permission bits (owner_exec
|| group_exec || other_exec).
13 new unit tests covering all categories, case insensitivity, hidden
files, and edge cases. 959 tests total, 0 failures.
vasilito
77750b5128